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Metallogenesis of the Totoral LCT rare-element pegmatite district, San Luis, Argentina: A review
Accepted Manuscript Metallogenesis of the totoral LCT rare-element pegmatite district, San Luis, Argentina: A review Miguel Ángel Galliski, María Florencia Márquez-Zavalía, Diego Sebastián Pagano PII:
S0895-9811(18)30365-1
DOI:
https://doi.org/10.1016/j.jsames.2018.12.018
Reference:
SAMES 2075
To appear in:
Journal of South American Earth Sciences
Received Date: 31 August 2018 Revised Date:
8 November 2018
Accepted Date: 20 December 2018
Please cite this article as: Galliski, Miguel.Á., Márquez-Zavalía, Marí.Florencia., Pagano, Diego.Sebastiá., Metallogenesis of the totoral LCT rare-element pegmatite district, San Luis, Argentina: A review, Journal of South American Earth Sciences (2019), doi: https://doi.org/10.1016/ j.jsames.2018.12.018. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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METALLOGENESIS OF THE TOTORAL LCT RARE-ELEMENT PEGMATITE
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DISTRICT, SAN LUIS, ARGENTINA: A REVIEW
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Miguel Ángel Galliski, 1,2 María Florencia Márquez-Zavalía, 3,4 Diego Sebastián Pagano.
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IANIGLA, CCT-CONICET Mendoza. Av. Ruiz Leal s/n (5500) Mendoza Argentina.
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Mineralogía y Petrología, FAD, Universidad Nacional de Cuyo, Centro Universitario,
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(5502) Mendoza, Argentina
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Departamento de Geología, Universidad Nacional de San Luis, Ejército de los Andes
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950, San Luis (5700), Argentina
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Rodríguez 273 (5502), Mendoza, Argentina.
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CeReDeTeC, Facultad Regional Mendoza, Universidad Tecnológica Nacional, Coronel
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[email protected]; [email protected];
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[email protected]
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Corresponding author:
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Miguel Ángel Galliski [email protected]; IANIGLA, CCT-CONICET,
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Mendoza. Av. Ruiz Leal s/n, Parque Gral. San Martín, (5500) Mendoza, Argentina. (54)
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261 524 4222
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ABSTRACT
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The Totoral Pegmatite District (TPD) is the southernmost rare-element LCT pegmatite field
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of the Pampean Pegmatite Province. The TPD produced intermittently in the last 60 years
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Ta-Nb ore minerals, spodumene, beryl and ceramic raw materials. It is located in the
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southern part of the Eastern Pampean Range of San Luis province. It was developed during
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the late stage of accretion of the Famatina terrane to the West Gondwana in the Lower
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Paleozoic (≈ 450 Ma). The parental S-type leucogranites and rare-element pegmatites of
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REL-Li subclass form three groups aligned NNE. The leucogranites were originated by
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muscovite (± incipient biotite) dehydration melting of preferably metapelites (±
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metagreywackes) of the Pringles Metamorphic Complex (PMC). The resultant bimodal
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suite of S-type muscovite-tourmaline and muscovite-biotite leucogranites show major, trace
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elements, and Pb-Ba ratios compatible with both low-T and higher-T collisional
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leucogranites. These leucogranites were emplaced after regional metamorphism in the
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upper part of the mica schists unit of PMC at 640-725 ºC and ≈400-500 MPa, and they
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fractionated to their associated pegmatites as is supported by the spatial association, similar
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age and fractionation trends of leucogranites and pegmatites. The regional integrated
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pegmatite zoning shows the sequence: leucogranite, pegmatitic leucogranite, barren-
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transitional to beryl-type, beryl-columbite-phosphate subtype, albite-spodumene type,
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complex-type spodumene-subtype and albite type rare-elements pegmatites. This zonation
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follows a path towards decreasing pressure of emplacement. The crystallization of
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pegmatites was triggered by the rapid undercooling provoked by the thermal contrast due to
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the fast forced emplacement in the hosting mica schists and the H2O and fluxes content of
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the melts that produced nucleation delay and high crystal growth rate of the minerals. The
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Li-bearing pegmatites have genetic links with the higher-T leucogranites. The emplacement
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of the pegmatites was facilitated by a shear zone, and they show synkinematic ductile-state
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deformation ascribed to the late stage of the Famatina terrane accretion. Later on, most of
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them were tectonically affected in brittle state by the diastrophism attributed to the
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westward accretion of the Cuyania terrane.
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Keywords: S-type leucogranite. LCT rare-element pegmatites. Ordovician. Famatina
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terrane collision. San Luis. Argentina.
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Abbreviations: TPD Totoral Pegmatite District; LCT Li-Cs-Ta: Lithium, Cesium
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Tantalum; CMC Conlara Metamorphic Complex; PMC Pringles Metamorphic Complex;
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NMC Nogolí Metamorphic Complex; LT Cerro La Torre; PR Paso del Rey; LA Loma Alta.
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1. INTRODUCCION
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The relationships between granites and consanguineous rare-element pegmatites of the
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petrogenetic LCT (Li-Cs-Ta) family of Černý and Ercit (2005) are many times obscured
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because they are usually found in different levels of the crust, and the erosion in little
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opportunities favors the observation of all of them in the same parental system. When the
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exposure allowed the observation, as it occurs in some places as Ghost Lake (Breaks and
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Moore, 1992), Harney Peak, Black Hills (Shearer et al., 1992) or Central Iberian zone
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(Roda-Robles et al., 2018), it is possible to establish a linkage that relates granites and
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pegmatites. In other districts, the integrated geological observations led researchers as
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Heinrich (1953) and Varlamoff (1972) to set patterns of regional zoning sketched by
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Trueman and Černý (1982), Černý (1991b) or London (2008). In these cases, the
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representativeness of the different kinds of pegmatites hardly reaches the ideal of the
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theoretical schemes. However, we think that this regional zoning represents the
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modifications produced throughout the process of fractional crystallization of the parental
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granites and the pegmatites and their description contributes to support the experimental
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results and helps to interpret the origin of these singular igneous rocks.
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In this paper we address the review of a pegmatite district that evolved in the western
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margin of Gondwana, which has the advantage of being located in a slightly tilted basement
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block that allowed the examination of the processes that happened in the upper part of the
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middle continental crust involving a thick sedimentary prism during an Eopaleozoic
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terrane-continent collision. The textures and the modal and chemical composition of the
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fertile granites are described and considered together with the main characteristics and
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distribution of the associated rare element pegmatites and the reasons of their metallogenic
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potential in lithium and tantalum mineralization. Previous studies about the district address
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the mineralogy and distribution of the pegmatites (Oyarzábal, 2004), the geochemistry of
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their K-feldspar and muscovites (Oyarzábal et al., 2009) and the age and origin of the
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associated granites (Steenken et al., 2006; López de Luchi et al., 2007). There is profuse
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complementary information background that tackle related specific points contributing to
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the understanding of the evolution of the district that will be quoted in due course.
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2. METHODOLOGY
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The cartography of the TPD was made with aerial photographs 1:20000 and planialtimetric
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restitution. Data collected and mapping of the main granitic pegmatites and description of
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the internal zonation was performed at different times always using the nomenclature
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established by Cameron et al. (1949) and Černý (1982). After inspection and description of
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the polished thin sections of medium grained granites and metamorphics, the modal
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compositions of leucogranites was obtained with a manual point counter using not less than
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1200 points per thin section. The modal count of the coarse- and pegmatitic-grained
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leucogranites was made on representative outcrops in the field and it is less precise that the one
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made in medium-grained facies under the microscope. The classification of the rocks was
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based in the IUGS system (Le Bas and Streckeisen, 1991) and the abbreviations of the
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minerals are after Whitney and Evans (2010). Major-, trace- and REE-analyses of whole
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rock powdered samples were done in Activation Laboratories Ltd. at Ancaster (Ontario).
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Sample digestion was done on Li-metaborate–tetraborate fused discs dissolved in weak
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nitric acid. Analyses were performed by ICP spectrometry (major elements) and ICP-MS
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(trace and REE). The detection limits for major elements were 0.01%, except for TiO2 and
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MnO (0.001%); for the following trace elements the detection limits were: Sc, Be, Co, Ga,
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Ge, Nb, Sn and W = 1 ppm; V, As and Pb = 5 ppm; Cr and Ni = 20 ppm; Cu = 10 ppm; Zn
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= 30 ppm; Rb, Sr, Y and Mo = 2 ppm; Zr = 4 ppm; Ag, Sb and Cs = 0.5 ppm; In and Hf =
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0.2 ppm; Ba = 3 ppm; La, Ce, Nd, Sm, Gd, Tb, Dy, Ho, Er, Yb, Ta, Tl, Th and U = 0.1
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ppm; Pr, Eu and Tm = 0.05 ppm; Lu = 0.04 ppm and Bi = 0.4 ppm.
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3. GEOLOGICAL SETTING
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The Totoral pegmatitic district (TPD) is located in the southwestern part of the San Luis range
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(Fig. 1A) that forms part of the Eastern Pampean Ranges. This range is a key location for
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understanding the geological processes occurring in the southwestern proto-margin of
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Gondwana, situation that has promoted in the past twenty years an increment in the research of
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the crystalline basement (see Morosini et al., 2017 and references therein). However, the rare-
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element granitic pegmatites are comparatively less studied even though they constitute most of
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the mineral resources that are being exploited in the area (Galliski, 1994a, b). The crystalline
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basement of the range was subdivided in three different NNE-SSW major elongated units that,
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from east to west, were named Conlara Metamorphic Complex (CMC), Pringles Metamorphic
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Complex (PMC) and Nogolí Metamorphic Complex (NMC) (Sims et al., 1997, 1998). The
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contact between these blocks is tectonic along ductile shear zones. The provenance studies
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(Steenken et al., 2004; Drobe et al., 2009) establish the differences among these units, and
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places the tectonic setting of sedimentation preferably in an active margin. They consider that
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the Th enriched metapsamites of PMC point to more felsic sources than the others, suggesting
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inputs from a recycled passive margin mixed with new felsic material. The PMC clastic
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sequence was sedimented in the western border of Gondwana from materials derived possibly
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from the Pampean orogeny or the Dom Feliciano/Gariep orogen (Drobe et al., 2009) during the
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Cambrian. The PMC was strongly folded developing a main penetrative foliation with NNE
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strike during the Famatinian orogeny. The PMC exposed sequence grades in a distance of
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approximately18 km from granulite facies locally developed in the contact with a belt of small
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mafic-ultramafic intrusives in the west, to amphibolite and greenschist facies eastward. The
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main lithologies comprise migmatites, gneisses, scarce amphibolites, mica schists with
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metaquartzites intercalations, phyllites and slates with minor intercalation of
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metaconglomerates (Perón Orrillo and Rivarola, 2014) arranged in NNE-SSW trending belts.
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According to Hauzenberger et al. (2001), the granulite facies with a paragenesis of Grt-Crd-Sil-
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Bt-Kfs-Pl-Qz-Rt±Opx reached PT conditions of 740-790ºC and 570-640 MPa during the
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M2(G) metamorphism. The migmatites, showing evidences of in situ melting, occur to the east
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of the granulites and grade eastward to gneisses. The paragenesis in this facies shows St-Grt-
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Bt-Ms-Pl-Qz-Ilm±Fi±Chl with peak conditions of 570-600ºC, 500-570 MPa reached during the
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M1(A) metamorphism (Hauzenberger et al., 2001). In the contact between the high and
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medium grade rocks, mylonites of the La Arenilla shear zone retrograde the granulite
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paragenesis to the amphibolite ones. The gneisses are in tectonic contact (sensu Sims et al.,
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1997; von Gosen, 1998; Ortiz-Suárez and Casquet, 2005) or grade (Ortiz-Suárez et al., 1992;
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Steenken et al., 2011) to a belt of mica schists that passes eastward to phyllites, ending with
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slates before the metamorphic grade increases again prior to the tectonic contact with the CMC.
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The mica schists were distinguished as a unit with this name (von Gosen, 1998) and they have
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tectonic boundaries with the phyllites and slates that were named San Luis Formation (Prozzi
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and Ramos, 1988). Sims et al. (1997), based in the different degree of deformation of the PMC
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and the San Luis Formation, considered that the late would be younger, and they mark the
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contact between the two units as a shear zone. However, detailed structural studies showed that,
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even though in several profiles there are reverse faults (von Gosen, 1998), possibly much of
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metasedimentary lithological units of the PMC and particularly the mica schists and the
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phyllites constitute, with structural discontinuities, a single crustal sequence and they will be
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considered as such (von Gosen, 1998; Steenken et al., 2006). The age of the M1 metamorphism
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was initially bracketed between 484±7 Ma and 451±10 Ma (Table 1, cf. Sims et al., 1998;
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Steenken et al., 2011 and references therein). However, recently Ferracutti et al., 2017 obtained
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two Nd-Sm isochrons that give 1289 (±97) and 1002 (±150) Ma for the high grade metaclastics
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and the ultramafic rocks respectively, that could indicate that in the western part of the PMC
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the outcrops of high grade rocks would be part of an older crystalline basement attributable to
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the lower crust.
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In the easternmost section of the mica schist belt, I- and S-type granites are emplaced, mostly
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arranged in the same NNE-SSW trend. The I-type granites are represented by the Pampa del
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Tamboreo granodiorite, dated by SHRIMP U-Pb in zircon at 470±5 Ma, that shows its western
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border affected by tectonism and the eastern side develops contact metamorphism in the San
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Luis Formation (Sims et al., 1997). In the studied area, the S-type granites form two main
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stocks named Cerro La Torre (LT) and Paso del Rey (PR) and a swarm of leucogranitic sills,
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dykes, pegmatites, and aplites distributed asymmetrically, mostly in the eastern flank of the
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granites (Galliski, 1994a). Sato et al. (2003) included them in their synorogenic granitoids
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respect to the Famatinian orogenesis. López de Luchi et al. (2007) studied some of these
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plutons grouped in their OGGS (Ordovician Granodiorite-Granite Suite) in the scope of the
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petrogenesis of the Paleozoic granitic rocks from the San Luis range. They subdivided the
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OGGS in high-T and low-T granites and proposed for the latter an origin based in biotite
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dehydration melting at low pressures of metagreywacke rocks, leaving plagioclase in the
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residue. The granites and pegmatite swarms show structural evidences of crystallization under
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a protracted compressive tectonic regime during the collisional Famatinian orogeny (ca. 500-
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440 Ma) that accreted, in a first episode, the Famatina Terrane to the Gondwana (Ramos,
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2010). Geochronology of the granites varies depending of the used method (Table 1). Llambías
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et al. (1991) dated by Rb-Sr isochron the Paso del Rey - Río de la Carpa granites in 454±21 Ma
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with 87Sr/86Sri of 0.712. Varela et al. (1994) obtained biotite ages from 372 to 391 Ma. Von
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Gosen et al. (2002) got a U-Pb zircon TIMS age of 608+26-25 Ma. Stenkeen et al. (2006)
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obtained a 207Pb/206Pb zircon evaporation ages of 597±54 and 491±19 Ma, meanwhile Stenkeen
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et al. (2006) dating by SHRIMP U-Pb the zircons of Paso del Rey north pluton obtained an
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upper intercept with the concordia at 456±30 Ma (MSWD = 0.26). In any case, the uncertainty
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produced by inherited zircons makes the determination of the crystallization age difficult. Since
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that the pegmatites associated with the Paso del Rey leucogranite intrude the granodiorite in
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Pampa del Tamboreo, the leucogranite data older than 470± 5 Ma have little confidence.
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Because of that, based on coincidence between the Rb-Sr isochron and the U-Pb age of
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Steenken et al. (2006), the probable age of the Paso del Rey leucogranite is considered ≈ 455±5
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Ma. The K-Ar biotite data of Varela et al. (1994) at 372 to 391 Ma are interpreted as the
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definitive cooling ages of the intrusive.
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4. THE S-TYPE LEUCOGRANITES
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4.1 Petrography
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The granites of the TPD form two irregular bodies named Cerro La Torre (LT) and Paso del
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Rey (PR) (Fig. 1B). Both are part of a larger S-type granite suite that also includes the
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Cerros Largos, La Florida and to the east, outside the studied area, the Río de la Carpa and
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Río Quinto plutons. Because most of the rare-element pegmatites are spatially associated
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with the PR and LT leucogranites, our study is heavily concentrated on them. To the south,
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the La Florida stock was studied by Carol et al. (2007) meanwhile Llambías et al. (1996)
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described the granitic rocks located to the north and east of the TPD. López de Luchi et al.
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(2007) consider samples of PR pluton in their low-T OGGS granites mentioned above.
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The LT granite is a small intrusive, built up by a few hundreds of lenses, sills and dikes that
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include deformed septa of metamorphics and has a few different petrographic variations. Its
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intrusion produced a partial metamorphic overprint in the hosting micaschist, which develops
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nodules of cordierite or muscovite -locally with fibrolite-, garnet and widespread
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tourmalinization. The two common petrographic types in the lenses are a light grey medium-
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grained rock (Fig. 2A) and a light-pink pegmatitic-grained rock (Fig. 2B). The medium-grained
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granite is formed by quartz (3-1 mm), plagioclase (An13-16) with bent twin planes, microcline (<
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5mm), and bent muscovite as the main accessory mineral. Garnet occurs in 1-2 mm euhedral
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grains and tourmaline is associated with late-stage quartz crystals. Biotite is present in the
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southern part of the leucogranite replaced by muscovite. In the contact with the metamorphics
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the grain size diminishes and euhedral crystals of muscovite are parallel to the schistosity. The
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pegmatitic facies form irregular lenses and areas with transitional borders. They are composed
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by coarse (20-30 cm) subhedral microcline crystals contained in a groundmass mostly formed
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by quartz and coarse-grained (up to 15 cm) muscovite with feathery habit. The most common
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accessory minerals are schorl in 5-7 cm sized crystals, garnet and, less frequently, anhedral
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apatite-supergroup minerals and monazite. Occasionally microcline is concentrated forming
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almost monomineralic meter-sized irregular domains. Albitization affects both facies
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developing, in irregular sectors, pervasive replacement formed by an assemblage of Ab-Qz
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(≈90%)-Ms±Grt-Ap-Tur. Albite (An4-8) shows up to 10 mm crystals with undulose extinction and
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bending, suggesting synkinematic crystallization. Late-stage quartz-feathery muscovite rich veins
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with schorl, apatite and Mn-Fe oxides fill joints in the NW part of the stock. In the central and
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southern parts of the intrusive there are frequent subspherical pods of pegmatitic differentiates up
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to 1 m diameter that contain euhedral crystals of garnet, schorl and muscovite. The finer- (Fig.
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3A, 3B) and pegmatitic-grained rocks have modes (Table 2) corresponding to monzogranite-
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granodiorite and alkalifeldspatic granite, respectively (Fig. 4). To the northeast of the LT
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leucogranite, the outcrops of pegmatitic leucogranite become more sporadic and form sub
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parallel lenses up to a hundred meter wide in the thicker parts, which are intruded and
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harmonically folded in the mica schists without evidences of associated rare-element
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pegmatites.
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The PR is a larger stock, of general ovoidal geometry with the main axis oriented N15-35ºE,
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and formed by irregular and major separated outcrops (Fig. 1B) composed by three different
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facies. To the east of the leucogranites, in the surroundings of San Luis pegmatite, the host
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rocks are composed by mica schists with phenoblasts of muscovite, garnet and staurolite
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contained in a groundmass of Ms-Qz-Bt-Chl-Pl±Ap-Tur-Zrn-Hem. The main rock of the PR
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pluton forms thick lenses (Fig. 2C) of light-gray to pinkish, medium-grained monzogranite
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composed of Qz+Kfs+Pl+Ms-Bt±Tur±Gr±Ap±Zrn±Mnz±(Sil). Quartz forms anhedral grains
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with undulose or fragmented extinction and myrmekitic intergrowths with plagioclase.
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Plagioclase (An12-24) occurs as subhedral, frequently bended, weakly zoned crystals. Microcline
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occurs as interstitial, late-stage, anhedral crystals that usually include the other phases, mostly
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quartz in optical continuity. Perthite intergrowths are infrequent. Muscovite forms up to 15 mm
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subhedral crystals, commonly bent, that occasionally include euhedral biotite. Locally, near the
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contact with the host rock, the muscovite and biotite contents increase and both minerals show
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subparallel orientation giving a very slight foliation. Tourmaline is present in the same areas
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where muscovite is abundant, in 1-2 cm prismatic crystals; garnet is usually irregularly
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associated with tourmaline or biotite in euhedral crystals and sometimes intergrown with
244
apatite (Fig. 3A, B). Zircon and monazite crystals are scarce. The sample M49 was taken 850
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m to the NW of the PR leucogranite in the western lens that crops out on the road La Arenilla -
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Paso del Rey. It is a different finer-grained leucogranite, foliated, garnet-bearing, and with
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lenses of sillimanite (fibrolite), disconnected from the PR main lenses. Fibrolite is also present
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in the northern part of the PR leucogranite and in the outcrops of some Loma Alta (LA) sills
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forming subparallel aggregates frequently associated with muscovite. Modal counts show that
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all the rocks are monzogranites and that in its central area the intrusive has higher Kfs/Pl ratios
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(Table 2, Fig. 4). Several types of quartz bearing or pegmatitic zoned dykes, up to one meter
252
wide and mostly subparallel to the main axis of the intrusive were described and considered
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cogenetic with the PR granite (Oyarzábal and Galliski, 1993).
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In the central and southern parts of the PR intrusive, a very coarse-grained to pegmatitic
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leucogranite that transitionally passes to the medium grained monzogranite is volumetrically
256
significant. This rock is formed by cm to m-sized perthitic K-feldspar megacrysts, occasionally
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including micrographic quartz, included in a Qz-Ms-Ab±Tur-Grt-Ap groundmass. Quartz
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forms milky to pink masses containing the other minerals. Muscovite occurs in two
259
generations: as up to 15 cm books included in quartz or K-feldspar, and including schorl, or as
260
small flakes pervasively replacing feldspars. Garnet occurs in 5-7 cm euhedral crystals usually
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immersed in quartz. Plagioclase is subordinate replacing K-feldspar with cleavelandite or
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sugary habit.
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In the eastern flank of the PR intrusive outcrop many lenses (<160 m thick, ~500 m length) of
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pegmatitic leucogranite separated from the main granite by decametric septa of schists. This is
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a light gray with pinkish hue rock with megacrysts of perthitic K-feldspar (Fig. 2D), sometimes
266
showing graphic texture, contained in a medium grained groundmass composed of Qz-Pl-Kfs-
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Ms±Tur-Grt-Ap. Close to the contact with the hosting mica schists occur small schlierens
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formed by tourmaline, biotite and garnet.
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Between the LT and the PR leucogranitic stocks occurs a dome, with its main axis oriented NE-
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SW known as LA. It is formed by many sills of pegmatitic leucogranites intercalated in the Bt-
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Ms- schists. The mica schists are crosscut by Qz-Pl-Ms cm wide veins with fibrous sillimanite
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growing in muscovite or in the interphase quartz-plagioclase. The eastern flank of the LA high
273
is the most heavily populated with lenses of pegmatitic leucogranite usually concordant with
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the schistosity of the folded host rocks. For comparison with other uplift situated to the east
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(e.g., Río de la Carpa leucogranite), these dome structures occur in the upper part of the
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leucogranite stocks.
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Comparing with other localities, the mineral composition and textures of the LT described
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rocks fit well with the muscovite-tourmaline leucogranites from the Harney Peak, South
279
Dakota (Norton and Redden, 1990), or High Himalaya leucogranites (e.g., Scaillet et al., 1990;
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Visonà and Lombardo, 2002), meanwhile the PR stock is built by muscovite-tourmaline and
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also muscovite-biotite leucogranites.
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4.2 Geochemistry
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A considerable fraction of the rocks that conform the TPD leucogranites are very coarse grained
284
to pegmatitic textured and introduce the problem on the representativeness of the samples. For
285
this reason, the whole-rock chemical analyses were performed only on medium to coarse-
286
grained facies. Pegmatitic facies were investigated based in some major and trace elements of
287
K-feldspar and muscovite (Oyarzábal et al., 2009). Table 3 displays the geochemical data for
288
samples of the LT and PR leucogranites and metamorphics from the PMC. With the exception
289
of sample LT25 the samples from LT and PR stocks have silica contents of 73.36 to 73.74 wt.%
290
SiO2 (avg. for both stocks, respectively), high alumina (14.96, 14.18 wt.% Al2O3), low values of
291
TiO2 (0.04, 0.04 wt.%), MgO (0.12, 0.17 wt.%), CaO (0.59, 0.67 wt.%), FeOT (0.65, 0.58
292
wt.%) and MnO (0.08, 0.12 wt.%). The average contents of Na2O is 3.97, 3.59 wt.% and of
293
K2O 4.55, 4.47 wt.% respectively. The average molar ratio of the granites show K/(K+Na) =
294
0.42, 0.45, and the average trace elements contents (ppm) of Ba 331, 190; Rb 124, 189, and Sr
295
83, 51 respectively. The Rb/Sr ratios are 0.5-4.4 and 2.1-5.5 for LT and PR plutons. These
296
rocks are high silica, strongly peraluminous granites with average ASI (Alumina Saturation
297
Index = Al/(Ca-1.67P+Na+K) values of 1.20 and 1.22 for LT and PR stocks, respectively. The
298
high ASI values and low Mg+Fe contents (Fig. 5) plot these rocks in the field of collisional
299
leucogranites (Nabelek and Liu, 2004). Among the four different types of rare-element granites
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recognized by Linnen and Cuney (2004) and Černý et al. (2005), the TPD leucogranites have
301
SiO2/P2O5 and Th/Zr ratios similar to their peraluminous intermediate phosphorous rare-
302
element granites (Fig. 6A, B).
303
The content of REE is overall low, with average ΣREE of 18.5 and 26.9 ppm for rocks of both
304
stocks, most of which are slightly LREE enriched (14.7 and 21.4 ppm, respectively). The Eu
305
negative anomaly is weak in three samples of LT (Eu/Eu* 0.4-0.7); the remaining samples have
306
positive anomaly up to 4.7 Eu/Eu*. Meanwhile, most of the PR rocks have moderate Eu
307
negative anomalies (Eu/Eu* 0.4-0.9) with one sample without it (Eu/Eu* 1). The chondrite
308
normalized patterns (Fig. 7A) are similar to the biotite-muscovite, and tourmaline leucogranites
309
from Harney Peak (Duke et al. 1992, Nabelek and Liu, 2004), with the difference of
310
enrichment in LREE and HREE in TPD samples. Figure 7A also shows the REE plots of the
311
three more characteristic samples of the PMC which are very similar to the average metapelites
312
composition from Zanskar, Himalaya (Ayres and Harris, 1997). We interpret that the weak
313
enrichment of TPD leucogranites in LREE and HREE is possibly due to the contents of
314
monazite (±apatite) and garnet (± zircon), respectively. The few europium positive anomalies,
315
not rare in pegmatitic layers of leucogranites as Calamity Peak (Harney Peak, South Dakota)
316
has been suggested that can be originated by that feldspar (1) were not important in the
317
fractionation process, (2) were may be locally accumulated or (3) the f(O2) may have increased
318
(Duke et al. 1992). The spider diagram (Fig. 7B) shows compared with peraluminous
319
intermediate phosphorous rare-element granites, a similar pattern with peaks slightly less
320
marked but showing similar behavior for Th, Ta, Ti and REEs.
321
We used the Zr and REEs contents of the leucogranites to calculate the temperature based in
322
the zircon saturation thermometry (TZr) of Watson and Harrison (1983) and LREE saturation
323
thermometry (TREE) proposed by Montel (1993). The results (Table 3) show values ranging
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from TZr 640-725 ºC for LT and 642-713 ºC for PR. The TREE gives values comprised between
325
603 and 698 ºC for LT and 621 to 727 ºC for PR. The results are plotted in the diagram of
326
Figure 8. The lowest temperatures correspond to TREE of samples LT07 (604 ºC) and M49
327
(621ºC) and are considered too low. Both are from thick leucogranitic lenses situated in the
328
NW direction away of the main plutons in PR and LT respectively.
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329
5. GEOLOGY AND TYPES OF THE RARE-ELEMENT PEGMATITES
331
The pegmatites of the TPD are distributed in three groups located mainly in the eastern
332
flank of the described granitic rocks which are known as Cerro La Torre, Loma Alta and
333
Paso del Rey pegmatitic groups (Oyarzábal et al., 2009). They coexist spatially with sills
334
and dykes of pegmatitic leucogranites. The criteria used to differentiate rare-element
335
pegmatites from pegmatitic leucogranites in this pegmatitic district attend basically to the
336
different internal zoning and accessory mineralogy of both kinds of rocks. Pegmatites have
337
relatively well developed zoning of the different internal units, coarser grain size and
338
discrete to significant presence of accessory rare-element minerals. Instead, pegmatitic
339
leucogranites lack of very well developed zoning, especially the quartz core zone, have
340
traces or scarce, if any, accessory rare-element minerals and the grain size is usually
341
smaller. They are similar to the simple pegmatites of Norton and Redden (1990) or London
342
(2008). Rare-element pegmatites are volumetrically very subordinate to pegmatitic
343
leucogranites, possibly less than 3% (see Fig. 1B), which is perfectly embraced in the
344
standards for other pegmatite fields as Harney Peak (≈ 2%, Norton and Redden, 1990). The
345
most important pegmatite bodies that were intermittently mined in the past for beryl,
346
tantalite, muscovite, K-feldspar, albite, quartz or a variable combination of them are quoted
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in the Table 4. These pegmatites have been classified in types and subtypes of the rare-
348
element class, following the systematic of Černý and Ercit (2005), based mainly in internal
349
structure, bulk composition, rock-forming and accessory minerals and geochemical
350
signature. The main types of pegmatites are: (1) barren-transitional to beryl type
351
pegmatites: e.g., La Vistosa (I, II, III, IV and V); (2) beryl type, beryl-columbite-phosphate
352
subtype pegmatites: e.g., Santa Ana, La Empleada, Los Aleros, Los Chilenitos, Ranquel
353
and Cacique Canchuleta; (3) complex type, spodumene subtype: San Luis II, Víctor Hugo;
354
(4) albite-spodumene type: San Luis I, La Teresaida (with some features of spodumene
355
subtype), Diana and Cargil, and (5) albite type: Independencia Argentina and Aquelarre
356
with Los Chilenitos, La Argentina and La Rioja sharing some characteristics. In terms of
357
economic rare-element mineralization these different types of pegmatites could be named
358
as barren (1), beryl-bearing (2), lithium-bearing (±Nb-Ta) (3, 4), and Nb-Ta albite-bearing
359
(5) pegmatites. All the pegmatites have, to a different degree, internal zoning.
360
The barren-transitional to beryl type pegmatites of the LA pegmatite group are hosted into
361
leucogranitic lenses (La Vistosa I) or mica schists. The emplacement has been in few cases
362
permissive to, mainly, forceful, with strong structural control by a sub-parallel joint pattern.
363
The largest pegmatite dyke is 12 m wide and 105 m long. All pegmatites are poorly zoned,
364
with a variable mineral composition that is: border (Qz-Ms-Pl±Grt), wall (Mc-Qz-Ab-
365
Ms>Bt±Tur-Grt-Ap), intermediate (Mc-Qz-Ms-Ab±Tur) and core (Qz±Brl) zones; some of
366
them have scarce beryl and <5 cm altered Mn-Fe phosphates (Colaianni and Oyarzábal,
367
2008).
368
The beryl-columbite-phosphate subtype of beryl type pegmatites are located in the
369
southeastern part of the LT granite, and at the southeastern area of the LA Group. The
370
pegmatite outcrops are 60-90 m long and less than 30 m wide, and occur as single tabular to
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lenticular bodies intruding with sharp contacts the mica schists. In the surroundings of
372
Santa Ana pegmatite the bodies are folded and segmented. They are moderately to well
373
zoned, showing the following units: border, wall, intermediate and core (Qz±Brl) zones.
374
The primary mineral association comprises Qz-Mc-Ab-Ms-Brl-Col-Tur-Ap-Grt. Huge
375
crystals of Kfs (La Empleada, Fig. 9A), or discrete (Santa Ana) to giant (Ranquel, Fig. 9B)
376
nodules of primary phosphate minerals of the triphylite-litiophilite or beusite-graftonite
377
series occur in the core-margin association. It is characteristic of the TPD, and even of the
378
Conlara pegmatite district to the north, the Mn >> Fe geochemical signature of the primary
379
phosphates. Exsolution (Hurlbut and Aristarain, 1968; Hatert et al., 2012), magmatic
380
replacement (Galliski et al., 2009) or hydrothermal reworking of these primary phases
381
originate interesting associations of Mn-Fe-(Al-Ca-Li) mineral phosphates as qingheiite,
382
zavalíaite, huréaulite, etc. Mining of these kinds of pegmatites was drifting from beryl in
383
the 50´ and 60´ of the last century to muscovite, feldspar and quartz of ceramic grade in
384
recent times.
385
The albite-spodumene type pegmatites occur in the southernmost part of the TPD emplaced
386
in mica-schists nearby the pegmatitic facies of the PR leucogranite. They have tabular
387
shape with high aspect ratio. The modal composition shows albite and quartz dominant
388
over spodumene and K-feldspar, and a homogeneous and symmetric internal structure, with
389
a dominant internal zone of microcline and spodumene crystals enclosed in a medium-
390
grained Ab-Qz-Spd±Ms-Ap-Grt groundmass. The prismatic microcline and spodumene
391
crystals display parallel orientation forming comb-structure approximately normal to the
392
strike of the pegmatite (San Luis I pegmatite, Fig. 9C). San Luis I and La Teresaida
393
pegmatites have been synkinematically intruded and folded during their emplacement
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showing usually straining and stretching along the strike and occasionally some incipient
395
development of the quartz core (La Teresaida).
396
The complex type, spodumene subtypes pegmatites are San Luis II and Víctor Hugo. San
397
Luis II is located in the core of some anticlinal crests of a folded albite-spodumene type
398
pegmatite, named San Luis I (Oyarzábal and Galliski, 1993). The internal structure is
399
complex, consisting of border (Ms-Qz±Bt-Grt-Ap), wall (Mc-Qz-Ms-Spd), intermediate
400
(Mc-Qz-Spd±Ms-Ab) and core (Qz) zones; spodumene forms giant prismatic crystals (~ 2
401
m long in San Luis II) hosted in the massive quartz of the core. Accessory triphylite-
402
lithiophilite in discrete nodules sometimes altered to mitridatite (Galliski et al., 1998) and
403
Ms-Ab replacement units contain tantalite-(Mn) as accessory minerals or scarce cassiterite,
404
as in Víctor Hugo pegmatite (Galliski and Černý, 2006). Most of the Li-bearing pegmatites
405
were mined for spodumene and presently are being explored for their lithium resources.
406
The albite type pegmatites are located in the southeastern area of the LT and in the northern
407
part of the PR groups. The most typical are Independencia Argentina (Galliski et al., 2015)
408
and Aquelarre, but Los Chilenitos, La Argentina, and La Rioja show intermediate features
409
between beryl and albite type pegmatites. They are tabular bodies, approximately 200 m
410
long and 5-20 m wide, emplaced in quartz-mica schists, with N35º-40ºE strike and 45º-
411
70ºW dip. Zoning is asymmetric, with border (Ab-Qz±Ms-Ap), wall (Qz-Ab), outer
412
intermediate (Ab-Qz±Ms), middle intermediate (Ab-Qz-Spd±Ms), inner intermediate (Ms-
413
Qz±Ab) and core (Qz±Ms) zones, and a fine-grained Ab-bearing replacement unit (Ab±Qz-
414
Ms-Ap-Col) (Fig. 9D). These pegmatites were mined for beryl, columbite, fine-grained
415
muscovite and albite.
416
The chemical composition of the columbite-group minerals show variations related to the
417
type of pegmatite (Fig.10). In general, pegmatites of complex type, spodumene subtype
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418
show the most evolved chemical trends towards increasing #Ta and #Mn. Albite-type
419
pegmatites have moderately evolved CGM that show rhythmic zoning.
420
6. DISCUSSION
422
6.1 Source and origin of the S-type leucogranites
423
The high ASI values and low Mg+Fe contents (Fig. 5) of TPD granitic rocks is particular of
424
collisional leucogranites showing the two different petrographic types: tourmaline-muscovite
425
and biotite-muscovite, common in other occurrences (e.g., Scaillet et al., 1990; Nabelek and
426
Liu, 2004). These properties as well as the high 87Sr/86Sri relationships of 0.712 (Llambías et al.,
427
1991), the trace element contents (Table 3), the REE pattern (Fig. 7), and the values of TZr and
428
TREER (Fig. 8) of the LT and PR rocks are typical of S-type leucogranites (London, 2008) and
429
approximately in the range of leucogranites elsewhere as Manaslú, Everest, Gangotri or
430
Yadong, Himalaya (e.g., Montel, 1993; Visonà and Lombardo, 2002; Gou et al., 2016).
431
As in other occurrences, these leucogranites are generated belatedly during compressional
432
deformation and metamorphism of the metasedimentary prism in the upper plate of the
433
collisional orogeny (Nabelek and Liu, 2004 and references therein). Most authors consider,
434
based on isotopic data, that the source rock is located in the lower levels of the same unit
435
that they intrude (e.g., Deniel et al., 1987; Patiño-Douce and Harris, 1998) without influx
436
from other sources (Hopkinson et al., 2017). This interpretation suggests that probably the
437
dominant source of the TPD granites are the metapelites (±metagreywackes) of the PMC,
438
which show macroscopic evidences of partial melting in the migmatites (this paper) at P-T
439
conditions up of 570-600 ºC, 500-570 MPa determined by Hauzenberger et al. (2001) in the
440
amphibolite facies, or 790 ºC -720 MPa in the paragneisses (Ortiz-Suárez and Casquet,
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2005). The LT, PR and similar leucogranites are built by addition of lenses, sills (Fig. 2C)
442
or laccoliths formed by the intrusion of episodic batches of melts (Harrison et al., 1999),
443
transferred from the source by shear zone systems (Brown and Solar, 1998; Solar et al.,
444
1998), that imprint some local thermic metamorphism to the host rocks. The origin of the
445
melts is adscribed to incongruent melting of the protoliths in disequilibrium conditions
446
(Harris et al., 1995). Their bimodal petrography, with muscovite-tourmaline and biotite-
447
muscovite facies (Guillot and Le Fort, 1995; Visonà and Lombardo, 2002), reflects their
448
origin and has been preferably attributed to low pressure (500-1000 MPa) fluid-absent
449
muscovite dehydration melting of metapelites the first, and to biotite dehydration melting
450
of metapelites or metagraywackes the second (see Nabelek and Liu, 2004). Dehydration
451
melting is the preferred origin because in fluid-present melting the resulting melts are of
452
trondhjemitic composition (Patiño-Douce and Harris, 1998). Besides, most of the Rb/Sr
453
values of the LA and PR are 2-5 higher than those produced by water-saturated melting
454
(Harris and Inger, 1992). At low pressures (400 to ≈ 1000 MPa) the muscovite dehydration
455
melting is produced at lower temperatures than biotite dehydration melting. Weighing the
456
mineral and chemical composition of the LT and PR leucogranites, we note that biotite is
457
almost absent in the first, and locally present in small quantity in the second. The calculated
458
temperatures (Table 3, Fig. 8) and the Ba vs Pb contents (Fig. 11) also indicate that LT is a
459
low-T S-type leucogranite according to Finger and Schiller (2012) and that PR shows
460
higher temperature of generation. Based on these attributes we interpret that the LT
461
leucogranite was produced dominantly by muscovite dehydration melting of the PMC
462
metapelites and the PR was produced by muscovite plus incipient biotite dehydration
463
melting of PMC metapelites and metagraywackes. The chemical composition of both, and
464
their metallogenic potential, is related to the mineral composition of the source and the
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mechanism of melting. Muscovite dehydration melting consumes muscovite, plagioclase
466
and tourmaline from the pelitic mica schists, leaving some monazite, possibly armoured in
467
biotite, in the restitic fraction which produce the REEs low contents, the flat profiles (Fig.
468
7, Nabelek and Bartlett, 1998), and yields a small volume of melt which is in agreement
469
with the size of the LT stock. The B, Rb, Cs, low Li and Ta, and variably Be content of the
470
rocks is provided by muscovite and tourmaline and impart the LCT signature to the melts
471
(Icenhower and London, 1995, 1996; Evensen and London, 2003; London, 2008). In the
472
case of biotite dehydration melting, the temperature is higher, the melt volume increases, as
473
well as the quantity of Li-Cs-Ta contained in both biotite and muscovite, and other trace
474
elements producing increasing rare-element fertility. Melting of biotite also produces
475
higher contents of transition elements that generates biotite in the crystallizing leucogranite,
476
constrained to a low or moderate B content (Nabelek et al., 1992; Guillot and Le Fort,
477
1995). Both processes of melting are frequently in disequilibrium and the melts generally
478
contain entrained crystals of zircon and occasional monazite which complicate the U-Pb
479
dating giving older ages (Harrison et al., 1999). Mayor fractionation of S-type melts as an
480
alternative model for the origin of leucogranite (e.g., Scaillet et al., 1990, 1995) is discarded
481
in TPD because grouped plots of mayor elements in Harker diagrams (not shown) and week
482
Eu anomalies in REEs diagram (Fig. 7A) precluded it. However, after emplacement, during
483
the crystallization of the leucogranites, crystal-melt fractionation was very active as shown
484
by the trace elements variation of the K-feldspars (Oyarzábal, 2004) and the dispersion of
485
LT data along the slope of the line that divides both leucogranite fields in Figure 11.
486
Regarding to the necessary heat for the generation of leucogranitic melts, Nabelek and Liu
487
(1999, 2004) evaluate and model some possibilities proposed by different authors as: (1)
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increment of geotherms in the “cold” upper plate of a thickened crust; (2) the same but in a
489
“hot” upper plate of a thickened crust; (3) decompression melting; (4) thinning of mantle
490
lithosphere; (5) shear heating. They favor the shear heating (or strain heating, see Nabelek
491
and Nabelek, 2014) as the mechanism that triggers the melting of the protolith,
492
predominantly of the overthrusted slab of the plate, in our case the PMC. This mechanism
493
should also explain why along the same belt of S-type leucogranites - LCT rare-element
494
pegmatites there are differences in the temperature of generation of the melts and in the
495
type of mineralization of the pegmatites between the northern Be-bearing LT and LA
496
groups, and the southern Li (Ta)-bearing PR group.
497
6.2 Genetic links between granites and pegmatites
498
The close location of the TPD pegmatites to the LT, LA and PR leucogranites is prima
499
facie suspect of some parental relationships. The distribution of the rare-element pegmatites
500
is clearly defining three groups located preferably in the eastern side of the leucogranites.
501
The pegmatites are forming an imperfect regional zoning focused in these three intrusive
502
centers, whose pattern follows the general scheme developed by several authors
503
(Varlamoff, 1955; Trueman and Černý, 1982; London, 2008), and became an additional
504
fact supporting the hypothesis of parental relationships.
505
Oyarzábal et al. (2009) studied the geochemistry of K-feldspars in the granites and
506
pegmatites of this district in order to check the variations in chemical composition along the
507
fractionation of the different kinds of pegmatites established by several authors in other
508
pegmatite districts (e.g., Gordiyenko, 1971, 1976; Černý, 1994), and following the range of
509
chemical variation sketched for the Pampean Pegmatite Province (Galliski et al., 1997).
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The results of the K/Cs versus Rb variation diagram (Fig. 12A) for example, shows a clear
511
fractionation trend from the Kfs of the leucogranite intrusives to the geochemically most
512
differentiated rare-element pegmatites of the albite type.
513
Likewise, the ages of granites and pegmatites are in good correlation (Table 1). The
514
mentioned Rb-Sr isochron of PR and Río de la Carpa leucogranites of 454 ± 21 Ma with
515
87
516
given by Steenken et al. (2008) for the PR stock are in agreement with the 450 +10-2 Ma
517
LA- ICPMS age for columbite from San Luis II pegmatite (von Quadt and Galliski, 2011),
518
the U-Pb chemical age of 460±15 Ma for uraninite from Santa Ana pegmatite (Linares,
519
1959), or the 444.5 ± 9.2 Ma obtained in muscovite from a pegmatite that cuts across the
520
PR leucogranite (López de Luchi et al., 2002). The older U-Pb zircon TIMS age of
521
608+26-25 Ma obtained by von Gosen et al. (2002) for the PR stock would be contaminated by
522
inherited zircons from the PMC protolith.
523
The excellent agreement between spatial relationships, geochemical fractionation trends
524
and ages points to a common origin of leucogranites, pegmatitic leucogranites and rare-
525
element pegmatites of the TPD as occur in other analogous systems worldwide (Černý,
526
1991b; Černý et al., 2005; Roda-Robles et al. 2018).
527
6.3 Conditions of emplacement and crystallization of the pegmatites
528
The temperature and pressure of emplacement and crystallization of the TPD rare-element
529
pegmatites vary depending of the type of pegmatite. The albite-spodumene type pegmatites
530
do not show petalite or squi (spodumene + quartz pseudomorphs after petalite) and this
531
limits their lower pressure of crystallization at the stability field of spodumene which is 600
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Sr/Sr86 ri ratios of 0.712 (Llambías et al., 1991) or the age of 456±30 Ma (MSWD 0.26)
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ºC at ≈ 350 MPa (London, 1984). This estimation is not discordant with the T-P data of
533
Ortiz Suárez and Casquet (2005) that is 594 ºC - 530 MPa for the peak metamorphism of
534
the mica schists and 550 ºC - 470 MPa for the fine grained mica schist in transit to
535
phyllites. The albite-spodumene pegmatites were emplaced in an open system and
536
crystallized synkinematically (Oyarzábal and Galliski, 1993) as the typical stress-related
537
textures show (Fig. 9C, Černý, 1991a). The beryl-type pegmatites were intruded and
538
crystallized in closed system being later deformed. The albite-type pegmatites were
539
intruded and crystallized mostly in a closed system sporadically opened for a new pulse or
540
degassing of volatiles (Galliski et al., 2015).
541
The regional zoning suggests that the trend of fractionation of the parental leucogranites is
542
reflected in the distribution of the different types of pegmatites in each group and, partially,
543
in the fractionation trends shown by the trace elements of the Kfs. This argument linked
544
with the timing of the relationship between crystallization-deformation gives the temporal
545
sequence of intrusion that would be: barren → beryl type → albite-spodumene type or
546
complex type spodumene subtype → albite type. It is clear from mapping that in this
547
direction diminishes the metamorphic grade of the host rock. Thus, the distance of intrusion
548
would be related to the interplay of temperature of the host rock with viscosity of the
549
pegmatitic melts, assuming that the emplacement was pressure-driven toward decreasing
550
isobars, as it seems that has happened in these LCT petrogenetic family of orogenic
551
pegmatites. The grain size of the leucogranites, pegmatitic leucogranites, and different
552
types of pegmatites also suggest that undercooling combined with the water content of the
553
melts were the key factor that controlled the observed textures, as is shown by experimental
554
works (Fenn, 1977; London, 1992, 2008, 2018; Webber et al., 1999; Baker and Freda,
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2001; Simmons and Webber, 2008; Nabelek et al., 2010; Sirbescu et al., 2017, Maneta and
556
Anderson, 2018).
557
6.4 Implication for the origin of the pegmatites
558
The rare-element pegmatites melts were generated by the long-lasting crystal-melt
559
fractionation process of the parental leucogranites, which happened in large individual
560
batches of melts or in the successive amalgamated batches of the episodic intrusions that
561
formed the incremental plutons. The pegmatitic melts enriched in alkalis, fluxes, and
562
incompatible elements, with lesser viscosity than the leucogranites, were intruded in the
563
hosting mica schists between 100 to 1000 m away in normal cases, or up to 2500 in albite-
564
type pegmatites.
565
The melt that produced the beryl-type pegmatites was more viscous than the corresponding
566
to the Li-bearing pegmatites and formed closer, thicker and shorter bodies with very coarse,
567
usually idiomorphic crystals of Kfs (Fig. 9A). They show higher contents of P in the Kfs
568
than other pegmatites (Fig. 12B) as well as giant nodules of primary Mn-Fe (Li)-
569
phosphates. These attributes suggest that in most of them it was active some residence time
570
in the crystallizing chamber, which could facilitate some immiscibility process that
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concentrated P, Mn, Fe and Li in an exsolved phase. The very low contents of Mn, Mg and
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Fe in the parental granites, insufficient to crystallize biotite in most of them and that drives
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boron close to or inside the host rocks of the granites and pegmatites to form schorl,
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contrast with the large nodules of Mn-Fe(±Li) phosphates, suggesting that some interaction
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with mass-exchange of Mn-Fe(±Mg) between pegmatite melts and the micaceous host rock
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could have been active.
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The Li-bearing pegmatites present in the PR group show that most of them crystallized
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under dynamic conditions as evidenced by the typical UST (unidirectional solidification
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textures) of the albite-spodumene type considered as synkinematic (Černý, 1991a). Their
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origin is linked with three possibilities: (1) higher initial contents of Li of the PR
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leucogranitic melts, (2) larger volume of the fractionated melt than in LT or LA
582
leucogranites, or (3) most protracted time of fractionation. It is possible that all these
583
factors had some influence but we prefer to stress the possibility that relates the higher Li
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mineralization of the PR group to the increased participation of biotite during the
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dehydration melting of the protolith, which would be caused by the higher temperature of
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origin of its parental melts.
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The extraction of the pegmatitic melts for reaching the regional zoning is still discussed
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(Shearer et al., 1992, London 2008). A model of vertical zoning in the leucogranite
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chamber with less viscous layers at the top that are extracted first, followed sequentially by
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the less evolved melts, has been suggested for Iberian pegmatites (Roda-Robles et al., 2016,
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2018). This model, useful to explain the links between pegmatites associated to large,
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batholithic intrusions, finds some inconsistences when applied to the TPD. Some of them
593
are: (1) the leucogranites do not show differentiated rocks that support some type of vertical
594
zoning, (2) the pegmatites do not show fractionation along the strike, as it is frequent in
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some pegmatites of Central Iberian zone (Roda-Robles et al., 2016), (3) the most evolved
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pegmatites of albite-type show less deformation than the more primitives of beryl type. We
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think that an alternative possible explanation for the regional pegmatite zoning of the TPD
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is that they are the result of a process where different batches of leucogranites were the
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parents of different pegmatites. The most feasible mechanism of extraction of the
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pegmatitic melts from the leucogranites would be by episodic tectonic squeezing. The
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composition of the different pegmatitic melts should be conditioned by the degree of
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fractionation of each batch at the time of extraction and its rare-element fertility. More
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detailed precise geochronological work is necessary to demonstrate this possibility.
604
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6.5 Relationships between pegmatites and tectonics
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The pegmatites of the TPD show evidences of deformation that happened during and after
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emplacement. Some of the observed fabrics features are: folding, fractures, bending,
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boudinage, stretching and strained textures. Folding is more developed in a long and
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narrow belt situated eastward of the leucogranites that join La Teresaida, San Luis, La
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Argentina, La Empleada and Santa Ana pegmatites. Some authors (Sims et al., 1997; von
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Gosen 1998) mapped a non-linear shear zone separating mica schist and phyllites. This
612
zone is defined by deformed mica schists, stretched intercalated leucocratic veins and
613
truncated foliations. There are also minor faults, folded (e.g., San Luis, La Teresaida) and
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locally fractured (La Teresaida, La Argentina, La Empleada) pegmatites that point to a
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strained, non-linear belt that bounds the fine-grained mica schist with the phyllites.
616
It is known that there is a close temporal and spatial link between synkinematic granitic
617
plutons and shear zones (Hutton and Reavy, 1992). Shear zones control ascent and
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emplacement of granitic magmas (Brown and Solar, 1998; Weinberg et al., 2004) and can
619
give rise to a number of low pressure sites, not only in pressure shadows around competent
620
rocks, but also in dilational jogs, pull-apart regions, shear zone terminations, or dilatational
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areas resulting from active, crosscutting shear zones (Weinberg et al., 2009 and references
622
therein).
623
The occurrence of pegmatites near and within the shear zone separating mica schists and
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phyllites suggests a temporal and spatial link between both. Thus, the emplacement of
625
pegmatitic melts was possibly favored by low pressure sites developed along this ductile
626
shear zone.
627
The ductile strain of the belt, active during the emplacement of the pegmatites, was
628
possibly promoted by the rheological changes occurred in the conjunct mica schists -
629
pegmatites, produced by the heating contributed by pegmatitic intrusives, whose
630
emplacement was facilitated by the stress released in the shear zone. This would explain the
631
eastward asymmetry of the pegmatite distribution (towards the shear zone) and that the
632
emplacement occurred during the latest compressional events. Eastward of the mentioned
633
deformed belt, the folding vanishes and the pegmatites show softer evidences as boudinage,
634
stretching and internal deformation (Independencia Argentina, La Rioja). Some examples
635
of folding and fracturing (Fig. 9E, F) show that the emplacement was a synkinematic,
636
forceful, polypulsatory process that in extreme cases dismembered some zones of
637
crystallizing pegmatites. Galliski (1994b) suggested that the leucogranites and parental
638
rare-element pegmatite systems seemed to predate the Famatinian terrane-continent
639
collision since they display abundant post-emplacement deformation evidences, in
640
disagreement with other pegmatite provinces where a late-stage timing of intrusion is
641
frequent (Černý, 1991b). However, nowadays we interpret that part of the tectonic
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deformation was produced in a ductile state at the end of the Famatina terrane collision, but
643
the later and superimposed stronger diastrophism was produced partially in brittle state
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during a second collisional episode, situated westward and attributed to the Cuyania
645
accretion (Ramos, 2010).
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7. CONCLUSIONS
648
The S-type leucogranites and associated LCT rare-element pegmatites of the TPD are the
649
results of the episodic anatexis occurred during the late stage of the Famatina terrane-
650
continent collision (≈450-460 Ma). The low-T leucogranites were produced by dominant
651
muscovite dehydration melting and the higher-T leucogranites by muscovite plus incipient
652
biotite dehydration melting of preferably metapelites (±metagraywackes) from the PMC.
653
The leucogranites were intruded in the upper levels of the metamorphic prism at
654
approximately 400-500 MPa. Fractionation of leucogranites derived from muscovite
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dehydration melts produced dominantly barren, beryl-type and albite-type rare-element
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pegmatites. Differentiation of the leucogranites produced by muscovite plus biotite
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dehydration melting generated preferably Li-bearing pegmatites of the albite-spodumene
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type or spodumene subtype. The regional zoning from leucogranites, pegmatitic
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leucogranites, barren, beryl-type, albite-spodumene, complex-type spodumene subtype and
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albite-type pegmatites follows a path toward lower pressures of emplacement and it reflects
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the fractionation trend of the leucogranites, and the progressive decreasing viscosity of the
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residual melts. A shear zone separating mica schist and phyllites geological units controlled
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the ascent and emplacement of the pegmatites. The crystallization of the pegmatites was
664
triggered by rapid undercooling, due to the thermic contrast between the temperatures of
665
the melt and the host-rock, resultant of their fast intrusion. High undercooling, combined
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with high H2O contents and initial subsaturation in volatiles of pegmatitic melts, produced
667
low nucleation rate and fast growth of crystals during periodic resetting of the system
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traduced in internal zoning achieved in closed chambers of the host rocks in ductile-state.
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Late stage saturation in H2O and other volatiles, possibly helped to produce part of the rare-
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element (Be, Nb-Ta) mineralization.
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ACKNOWLEDGEMENTS
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Several grants of CONICET through different periods and PICT 21638 of FONCYT
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financed partially the research and are thanked. Teaching, conversations, and insights from
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many members of the PIG (Pegmatite Interested Group) through the years helped to season
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the background knowledge and are deeply appreciated. The authors are also very grateful
677
for the constructive reviews of Raúl Lira and Encarnación Roda-Robles. The editorial
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handling and comments of Víctor Ramos are much appreciated.
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Table 1: Compilation of the most significant dating ages of rocks for the Pringles Metamorphic Complex and the TPD evolution Area Location Rock Sample Method Rock/Mineral Age (Ma) ± 2σ My Reference Virorco Mafic complex Sm-Nd Isochron Whole rock 1002 150 Ferracutti et al. (2017) Metaclastics Sm-Nd Isochron Whole rock 1289 97 Ferracutti et al. (2017) Las Aguilas Felsic seg. in pyrox. JS080f U - Pb SHRIMP Zircon 478 6 Sims et al. (1998) Western Sector Grt-Sil-Gneiss JS129c Th-Pb SHRIMP Monazite 451 10 Sims et al. (1998) Felsic orthogneiss JS079 U-Pb SHRIMP Zircon 484 7 Sims et al. (1998) Mylonite A 56-01 U - Pb SHRIMP Zircon 498 10 Steenken et al. (2011) P. del Tamboreo Granodiorite U - Pb SHRIMP Zircon 470 5 Sims et al. (1997) Paso del Rey Leucogranite Rb - Sr Whole rock 454 21 Llambías et al. (1991) Paso del Rey Leucogranite U - Pb TIMS Zircon 608 +26-25 von Gosen et al. (2002) Paso del Rey N. Leucogranite U - Pb SHRIMP Zircon 456 30 Steenken et al. (2006) Paso del Rey Leucogranite A 02-02 207Pb - 206Pb Evaporation Zircon (older) 597 54 Steenken et al. (2008) Paso del Rey Leucogranite A 02-02 207Pb - 206Pb Evaporation Zircon (rims) 491 19 Steenken et al. (2008) Paso del Rey Leucogranite SLG1 K - Ar Biotite 381 13 Varela et al. (1994) Paso del Rey Leucogranite SLG8 K - Ar Biotite 372 20 Varela et al. (1994) Río La Carpa Leucogranite SLG9 K - Ar Biotite 391 9 Varela et al. (1994) Pegmatite A2-01 K - Ar Muscovite 407.8 8.3 Steenken et al. (2008) Eastern Pegmatite A6-01 K - Ar Muscovite 394.8 8.1 Steenken et al. (2008) Sector Pegmatite A10-01 K - Ar Muscovite 437.5 9.5 Steenken et al. (2008) Pegmatite A15-01 K - Ar Muscovite 408.4 8.6 Steenken et al. (2008) Paso del Rey Pegmatite AH-7 K - Ar Muscovite 398.2 9.2 Lopez de Luchi et al. (2002) Paso del Rey Pegmatite AH-8 K - Ar Muscovite 444.5 9.2 Lopez de Luchi et al. (2002) Victor Hugo Pegmatite VIC-01 K - Ar Muscovite 503 24 Galliski and Linares (1999) C. Canchuleta Pegmatite CAN-01 K - Ar Muscovite 433 24 Galliski and Linares (1999) San Luis I Pegmatite SLI-01 K - Ar Muscovite 317 33 Galliski and Linares (1999) Sta. Ana Pegmatite U - Pb Chemical Uraninite 455 23 Linares (1959) Sta. Ana Pegmatite U - Pb Isotopic Uraninite 460 15 Linares (1959) San Luis II Pegmatite U - Pb LA-ICP-MS Columbite 450 +10-2 v. Quadt and Galliski (2011)
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M AN U TE D EP
LT15a LT15b LT16a LT17a LT4c LT5a LT7a LT8c LT10b PR01 PR7 PR8 PR9 PR49 PR353 PR354 PR355 PR357 PR360
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Sample
ACCEPTED MANUSCRIPT Table 2: Modal compositions from Cerro La Torre (LT) and Paso del Rey (PR) leucogranites Main minerals Accessories Location Texture Grain size Minor Acc. Kfs Qz Pl Ms Bt Tur-Grt-Ap northern sector granular hypid. coarse 44.7 16.5 36.1 2.7 0.0 tr northern sector granular hypid. coarse 46.1 32.0 15.5 6.4 0.5 tr northern sector pegmatitic very coarse 37.7 54.4 0.0 5.5 3.0 Srl 2.4 northern sector pegmatitic very coarse 42.0 46.0 0.0 12.0 0.0 tr central sector granular hypid. medium 40.1 53.3 0.2 6.4 0.0 tr central sector pegmatitic very coarse 32.7 55.2 1.2 10.7 0.0 Srl .1 central sector granitic to peg. medium - very coarse 43.3 49.4 0.0 7.3 0.0 tr central sector granular hypid. medium to coarse 31.5 61.1 0.2 7.3 0.0 tr central sector granular hypid. medium 32.7 62.1 0.0 4.8 0.0 Grt .4 central sector granular hypid. medium to coarse 36.4 23.5 27.8 10.3 0.9 Srl 1.1 central sector granular hypid. medium to coarse 33.1 32.2 29.6 4.0 0.4 Srl 0.0, Grt 0.5, Ap 0.2 central sector granular hypid. medium to coarse 36.2 25.4 26.4 9.4 0.9 Srl 0.5, Grt 1.0, Ap 0.2 central sector granular hypid. medium to coarse 37.7 27.9 21.6 9.7 1.6 Srl 0.0, Grt 1.3, Ap 0.2 central sector granular hypid. medium to coarse 40.6 23.7 21.5 0.8 0.0 Srl 0.0, Grt 0.5, Sill 12.8 SE sector pegmatitic coarse to very coarse 27.7 53.2 14.6 3.02 0.0 Srl 1.3 Grt 0.2 SE sector granular hypid. medium to coarse 32.6 48.3 11.3 6.4 0.0 Srl 1.4 SE sector pegmatitic coarse to very coarse 34.9 47.6 7.6 4.9 0.0 Srl 5.0 SE sector pegmatitic coarse to very coarse 38.9 45.9 3.6 6.0 0.0 Srl 5.3, Ap 0.2 SE sector pegmatitic very coarse 37.6 47.4 5.9 6.2 0.0 Srl 2.9, Grt 0.09
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Table 3: Chemical Analyses of granitic and metamorphic rocks of the Totoral Pegmatite District Paso del Rey Stock R. Gde. Arenilla Santo Domingo Cerro La Torre Stock1 LT 13 LT 20 LT 25 LT 30 LT07 LT08 AVG M49 M7 M8 M9 M10 PR001 AVG M45 M48 M15 M12 TMLGR TMLGR 2MLGR 2MLGR TMLGR TMLGR TMLGR TMLGR 2MLGRTMLGR TMLGR TMLGR Migm. Gneiss Schist Phyllite 76.34 0.03 13.92 0.58 0.52 0.06 0.10 0.82 4.74 2.36 0.14
63.75 0.07 20.77 1.08 0.97 0.11 0.23 0.62 5.68 6.19 0.33
76.50 0.02 14.10 0.64 0.58 0.05 0.11 0.62 5.67 1.22 0.16
74.64 0.04 13.62 0.54 0.49 0.03 0.08 0.11 1.57 8.05 0.14
74.57 0.03 13.98 0.86 0.77 0.22 0.11 0.84 3.32 4.53 0.12
73.10 0.01 14.27 0.54 0.49 0.26 0.08 0.83 2.99 5.29 0.16
73.22 0.03 13.60 0.57 0.51 0.13 0.13 0.66 3.07 5.49 0.44
73.39 0.04 14.19 0.74 0.67 0.10 0.16 0.47 3.88 4.01 0.38
73.80 0.06 13.99 0.69 0.62 0.06 0.23 0.75 3.64 3.48 0.27
97.49
99.09
98.83
99.09
98.82
98.58
K ppm Ba Rb Sr Cs Ga Tl Be Ta Nb Hf Zr Y Th U W Sn Sb As Cr Ni Co Sc V Cu Pb
41174 19591 51385 10128 66825 37605 37785 43914 45574 33288 28889 225 28 216 12 965 542 331 26 184 132 273 131 52 254 56 155 94 124 112 232 203 156 70 28 58 15 153 174 83 21 46 47 76 6 2 7 3 2 2 4 2 8 10 10 11 10 19 12 9 8 12 8 10 12 12 1 0 1 0 1 0 0 1 1 1 1 1 2 8 6 <1 2 4 <1 3 6 8 1 0 2 1 0 1 1 0 1 2 4 7 5 15 9 5 6 8 1 5 19 10 1 2 2 1 2 1 2 2 1 2 1 33 61 69 19 64 21 45 41 31 53 34 5 5 16 5 2 3 6 1 9 16 12 1 1 3 2 7 1 2 0 1 3 2 1 2 3 2 3 4 3 2 2 2 2 6 1 2 1 1 1 2 1400 1380 1120 1060 4 3 10 3 3 2 4 2 2 6 2 13 <5 <5 <5 <5 <5 <5 <5 <5 <5 6 <5 24 <5 <5 <5 <5 <5 <5 <5 140 130 30 130 110 80 103 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 1 1 1 1 1 1 1 181 158 126 101 2 1 5 0 4 2 2 1 3 3 4 2 2 5 1 2 2 2 2 2 2 6 5 5 5 5 5 5 5 2 2 30 2 55 33 70 18 124 112 69 35 26 21 34
74.93 0.06 14.34 0.71 0.64 0.05 0.19 0.79 3.83 4.29 0.27
1.01 98.54
1.27 98.61
1.16 98.52
1.48 1.31 98.45 100.77
35613 275 211 75 8 12 1 9 2 8 1 32 10 2 2 1200 5 <5 <5 10 10 123 4 10 10 26
AC C
EP
TE D
73.36 0.04 14.96 0.72 0.65 0.08 0.12 0.59 3.97 4.55 0.17
74.00 0.06 14.70 0.90 0.81 0.12 0.23 0.49 4.15 4.27 0.28 0.65
73.74 0.04 14.18 0.69 0.58 0.12 0.17 0.67 3.59 4.47 0.30 0.65
73.42 0.61 11.98 3.40 3.06 0.06 1.29 1.29 2.08 3.73 0.09 0.85
58.83 0.94 16.50 8.83 7.95 0.17 3.10 0.54 0.82 3.63 0.09 5.48
64.74 0.74 15.53 5.82 5.24 0.15 2.66 0.67 1.62 3.21 0.13 3.63
61.24 0.82 18.06 6.72 6.05 0.08 2.32 0.31 1.77 4.06 0.15 4.34
98.80
98.93
98.90
99.87
RI PT
74.37 0.03 13.35 0.62 0.56 0.01 0.11 0.5 2.86 4.96 0.15 0.53
M AN U
SiO2 % TiO2 Al2O3 Fe2O3 FeOt calc. MnO MgO CaO Na2O K2O P2O5 LOI H2O wt. Total
SC
Location Sample Rock
99.85
250 220 40 17 --10 2 8 1 20 8 2 2 5 -0 1 170 5 5 3 8 5 32
37456 30964 30134 26647 33703 190 787 471 433 535 189 141 185 145 189 51 182 48 85 69 9 3 10 10 13 11 13 26 19 24 1 0 1 0 1 7 <1 3 3 4 2 1 1 2 2 9 14 17 15 17 1 8 6 5 5 35 298 194 168 164 9 21 35 16 34 2 15 19 13 17 2 3 4 4 3 1028 316 443 895 136 2 7 5 7 0 <5 <5 <5 <5 1 <5 <5 <5 <5 37 40 80 70 80 9 10 30 30 40 116 29 64 107 41 3 8 18 14 17 5 61 138 97 119 8 2 2 20 40 29 15 3 7 13
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10
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13
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10
10
10
10
24
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La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
2.2 4.2 0.5 1.6 0.4 0.2 0.5 0.1 0.7 0.1 0.4 0.1 0.6 0.1
3.2 5.4 6.0 1.9 0.5 0.1 0.5 0.1 0.8 0.1 0.5 0.1 0.8 0.1
6.8 13.2 1.4 5.1 1.5 0.3 1.6 0.4 2.6 0.5 1.5 0.3 2.0 0.3
5.0 8.9 1.0 3.3 0.8 0.1 0.6 0.1 0.8 0.1 0.4 0.1 0.7 0.1
1.6 2.7 0.3 1.0 0.2 0.3 0.2 0.1 0.3 0.1 0.2 0.1 0.4 0.1
4.3 7.2 0.7 2.2 0.5 0.3 0.3 0.1 0.5 0.1 0.4 0.1 0.9 0.1
3.9 6.9 0.7 2.5 0.7 0.2 0.6 0.2 1.0 0.2 0.6 0.1 0.9 0.1
2.2 4.0 0.4 1.0 0.2 0.1 0.2 0.1 0.5 0.1 0.5 0.1 1.1 0.2
4.2 8.3 0.9 3.2 0.9 0.3 0.9 0.2 1.6 0.3 0.9 0.1 1.1 0.1
7.5 16.5 1.9 7.0 1.9 0.2 1.4 0.5 2.8 0.5 1.5 0.2 1.3 0.2
5.2 11.0 1.2 4.6 1.3 0.3 0.9 0.3 2.0 0.4 1.1 0.2 1.2 0.2
6.3 12.9 1.4 4.9 1.4 0.4 1.2 0.4 2.2 0.4 1.2 0.3 1.3 0.2
4.2 9.0 -4.0 1.0 0.3 -0.2 ----1.2 0.2
4.9 10.3 1.1 4.1 1.1 0.3 0.9 0.3 1.8 0.3 1.0 0.2 1.2 0.2
37.4 78.7 9.2 36.6 7.3 1.3 5.3 0.8 4.2 0.8 2.1 0.3 2.3 0.3
47.4 99.6 10.9 43.3 8.6 1.5 6.7 1.2 6.4 1.3 3.5 0.5 3.4 0.5
12.3 60.8 2.7 9.3 2.0 0.4 1.7 0.4 2.7 0.7 2.3 0.4 2.7 0.4
50.1 100.0 10.7 37.5 7.7 1.4 6.2 1.1 6.4 1.3 3.6 0.6 3.6 0.5
∑REE LREE HREE (La/Lu)N (La/Sm)N (Lu/Gd)N Eu/Eu*
11.6 8.9 2.6 2.6 3.4 1.4 1.4
14.7 11.6 3.0 3.1 4.0 1.7 0.7
37.5 28.0 9.2 2.6 2.8 1.4 0.6
22.0 19.0 2.9 5.3 3.9 1.3 0.4
7.5 5.8 1.4 2.4 5.0 2.8 4.7
17.7 14.9 2.5 3.5 5.4 3.4 2.1
18.5 14.7 3.6 3.2 4.1 2.0 1.7
10.6 7.8 2.8 1.4 6.9 6.7 0.9
23.1 17.5 5.3 3.2 2.9 1.2 1.0
43.4 34.8 8.4 4.7 2.5 1.0 0.4
29.9 23.3 6.3 3.0 2.5 1.6 0.8
34.4 26.9 7.1 3.7 2.8 1.2 0.8
20.1 18.2 1.6
26.9 21.4 5.2 3.2 3.5 2.3 0.8
186.6 169.2 16.1 12.0 3.2 0.5 0.6
234.8 209.8 23.5 10.4 3.4 0.6 0.6
98.8 87.1 11.3 3.2 3.8 1.9 0.7
230.7 206.0 23.3 10.6 4.1 0.6 0.6
ASI FeO+MgO K/(K+Na) K/Rb Nb/Ta #Ta Zr/Hf Rb/Sr Rb/Ba Rb/Cs TºC (Zr) TºC (REE)
1.20 0.67 0.53 314.3 14.0 0.07 27.5 1.9 0.6 21.8 679 634
1.19 0.62 0.25 376.8 12.5 0.07 30.5 1.9 1.9 23.6 721 645
1.24 1.20 0.42 202.3 7.9 0.11 30.0 4.4 1.2 37.9 716 698
1.22 0.69 0.12 180.9 8.2 0.11 23.8 3.7 4.7 18.7 641 680
1.20 0.57 0.77 431.1 16.7 0.06 30.5 1.0 0.2 67.4 725 603
1.11 0.88 0.44 400.1 12.0 0.08 23.3 0.5 0.2 62.7 640 648
1.20 0.77 0.42 317.6 11.9 0.08 27.6 1.5 1.4 38.7 696 659
1.19 0.57 0.54 392.1 3.3 0.23 25.6 5.3 4.3 65.9 691 621
1.17 0.64 0.54 196.4 4.5 0.18 28.2 5.0 1.3 29.7 667 663
1.28 0.83 0.40 164.0 8.6 0.10 35.3 4.3 1.5 21.6 713 727
1.30 0.85 0.39 185.2 2.6 0.28 28.3 2.1 0.6 16.4 683 700
1.19 0.83 0.42 168.8 4.7 0.18 29.1 2.8 0.8 25.1 672 697
1.22 0.23 0.40 0.0 4.4 0.18 15.4 5.5 0.9 13.0 642 673
1.22 0.66 0.45 184.4 4.8 0.19 27.0 3.7 1.6 28.6 680 687
1.24
2.68
2.16
2.35
0.54 219.6 15.6 0.06 38.2 0.8 0.2 41.5
0.74 162.9 12.1 0.08 34.6 3.9 0.4 17.8
0.57 183.8 10.0 0.09 34.3 1.7 0.3 13.9
0.60 178.3 10.6 0.09 34.2 2.7 0.4 14.7
2
SC
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EP
AC C
1
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Zn
Major and trace elements of LT analyses were taken from Oyarzábal (2004). PR001 results were taken from Galliski (1994b). Great part of the high W, Cr and Co contents of PR leucogranites and metamorphics is due to contamination during milling with a WC ring mill equipment.
ACCEPTED MANUSCRIPT Table 4: Main rare-element pegmatites of the Totoral pegmatite district 80 62 150 30 22 55 15 190 >300 120 90 105 23 23 43 14.5 50 55 35 ~10 32 70 45 90 22 48 50 150 50 730 20 98 32 45 18
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Type
Subtype
15 Beryl Brl-Col-Pho 32 Beryl Brl-Col-Pho 42 Beryl Brl-Col-Pho 6 Beryl Brl-Col-Pho 14 Beryl Brl-Col-Pho 21 Beryl Brl-Col-Pho 8 Beryl Brl-Col-Pho 12 Albite 30 Albite 21 Beryl Brl-Col-Pho 7 Beryl Brl-Col-Pho 12 Barren (Brl) 4 Barren (Brl) 7.5 Barren 5.5 Barren (Brl) 4 Barren 20 Beryl Brl-Col-Pho 25 Beryl (Brl-Col) 6 Beryl (Brl-Col) 2 Beryl (Brl-Col) 5.5 Beryl (Brl-Col) 20 Beryl Brl-Col-Pho 15 Beryl (Brl-Col) 12 Beryl (Brl-Col) Beryl (Brl-Col) 5 Beryl (Brl-Col) 4 Beryl (Brl-Col) 6 Beryl 4 4 Complex Spodumene 2 to 35 Ab-Spodumene 7 Complex Spodumene 5 Ab-Spodumene 4 Ab-Spodumene 6 Complex Spodumene 5 Complex Spodumene
Mined for
Mining state
Brl Brl-Kfs-Ms Brl-Kfs-Ms Brl-Kfs-Ms Brl Brl-Kfs-Col Brl Ms-Ab Ab-Brl-Col Brl Brl-Kfs Kfs-Qz-Ms Kfs-Qz -Ms Kfs-Qz -Ms not mined Kfs-Qz -Ms Brl-Kfs-Qz Brl Brl Ms Brl Brl-Kfs-Qz Brl-Kfs Brl-Ms Tant Brl Brl Brl Spd Spd Spd Spd Spd Spd Col-Spd
inactive temp. active temp. active temp. active inactive inactive inactive inactive inactive inactive inactive active inactive inactive inactive inactive inactive inactive inactive inactive inactive inactive inactive inactive inactive inactive inactive inactive exploration exploration exploration exploration exploration inactive inactive
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tabular elipsoidal tabular lenticular lenticular tabular lenticular tabular subtabular tabular tabular tabular tabular tabular tabular tabular lenticular tabular tabular tabular tabular tabular tabular tabular tabular tabular tabular tabular tabular tabular tabular tabular lenticular lenticular tabular
Width
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Length
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La Titina Santa Ana La Empleada Los Aleros Devel Cerro La Torre Los Chilenitos Nueve de Julio Aquelarre Ind. Argentina La Betita La Tinita La Vistosa La Vistosa II La Vistosa III La Vistosa IV La Vistosa V Ranquel Loma Alta Ranquel II Don Lito San Ign. Loyola La China C. Canchuleta Tito San Cayetano La Argentina Franci Juan Héctor La Rioja San Fernando Paso del Rey San Luis I San Luis II Teresaida La Nilda Diana Víctor Hugo
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Title: METALLOGENESIS OF THE TOTORAL LCT RARE-ELEMENT PEGMATITE DISTRICT, SAN LUIS, ARGENTINA: A REVIEW
The TPD is formed by S-type leucogranites and rare-element pegmatites.
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Highlights:
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• The leucogranites form an Ordovician bimodal suite of anatectic collisional origin.
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Regional pegmatite zoning follows the fractionation trend of the parental granites.
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The Li-Ta resources are linked to pegmatites fractionated from high-T
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leucogranites.
S0895-9811(18)30365-1
DOI:
https://doi.org/10.1016/j.jsames.2018.12.018
Reference:
SAMES 2075
To appear in:
Journal of South American Earth Sciences
Received Date: 31 August 2018 Revised Date:
8 November 2018
Accepted Date: 20 December 2018
Please cite this article as: Galliski, Miguel.Á., Márquez-Zavalía, Marí.Florencia., Pagano, Diego.Sebastiá., Metallogenesis of the totoral LCT rare-element pegmatite district, San Luis, Argentina: A review, Journal of South American Earth Sciences (2019), doi: https://doi.org/10.1016/ j.jsames.2018.12.018. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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METALLOGENESIS OF THE TOTORAL LCT RARE-ELEMENT PEGMATITE
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DISTRICT, SAN LUIS, ARGENTINA: A REVIEW
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Miguel Ángel Galliski, 1,2 María Florencia Márquez-Zavalía, 3,4 Diego Sebastián Pagano.
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IANIGLA, CCT-CONICET Mendoza. Av. Ruiz Leal s/n (5500) Mendoza Argentina.
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Mineralogía y Petrología, FAD, Universidad Nacional de Cuyo, Centro Universitario,
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(5502) Mendoza, Argentina
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Departamento de Geología, Universidad Nacional de San Luis, Ejército de los Andes
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950, San Luis (5700), Argentina
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Rodríguez 273 (5502), Mendoza, Argentina.
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CeReDeTeC, Facultad Regional Mendoza, Universidad Tecnológica Nacional, Coronel
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[email protected]; [email protected];
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[email protected]
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Corresponding author:
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Miguel Ángel Galliski [email protected]; IANIGLA, CCT-CONICET,
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Mendoza. Av. Ruiz Leal s/n, Parque Gral. San Martín, (5500) Mendoza, Argentina. (54)
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261 524 4222
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ABSTRACT
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The Totoral Pegmatite District (TPD) is the southernmost rare-element LCT pegmatite field
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of the Pampean Pegmatite Province. The TPD produced intermittently in the last 60 years
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Ta-Nb ore minerals, spodumene, beryl and ceramic raw materials. It is located in the
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southern part of the Eastern Pampean Range of San Luis province. It was developed during
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the late stage of accretion of the Famatina terrane to the West Gondwana in the Lower
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Paleozoic (≈ 450 Ma). The parental S-type leucogranites and rare-element pegmatites of
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REL-Li subclass form three groups aligned NNE. The leucogranites were originated by
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muscovite (± incipient biotite) dehydration melting of preferably metapelites (±
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metagreywackes) of the Pringles Metamorphic Complex (PMC). The resultant bimodal
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suite of S-type muscovite-tourmaline and muscovite-biotite leucogranites show major, trace
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elements, and Pb-Ba ratios compatible with both low-T and higher-T collisional
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leucogranites. These leucogranites were emplaced after regional metamorphism in the
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upper part of the mica schists unit of PMC at 640-725 ºC and ≈400-500 MPa, and they
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fractionated to their associated pegmatites as is supported by the spatial association, similar
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age and fractionation trends of leucogranites and pegmatites. The regional integrated
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pegmatite zoning shows the sequence: leucogranite, pegmatitic leucogranite, barren-
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transitional to beryl-type, beryl-columbite-phosphate subtype, albite-spodumene type,
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complex-type spodumene-subtype and albite type rare-elements pegmatites. This zonation
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follows a path towards decreasing pressure of emplacement. The crystallization of
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pegmatites was triggered by the rapid undercooling provoked by the thermal contrast due to
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the fast forced emplacement in the hosting mica schists and the H2O and fluxes content of
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the melts that produced nucleation delay and high crystal growth rate of the minerals. The
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Li-bearing pegmatites have genetic links with the higher-T leucogranites. The emplacement
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of the pegmatites was facilitated by a shear zone, and they show synkinematic ductile-state
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deformation ascribed to the late stage of the Famatina terrane accretion. Later on, most of
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them were tectonically affected in brittle state by the diastrophism attributed to the
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westward accretion of the Cuyania terrane.
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Keywords: S-type leucogranite. LCT rare-element pegmatites. Ordovician. Famatina
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terrane collision. San Luis. Argentina.
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Abbreviations: TPD Totoral Pegmatite District; LCT Li-Cs-Ta: Lithium, Cesium
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Tantalum; CMC Conlara Metamorphic Complex; PMC Pringles Metamorphic Complex;
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NMC Nogolí Metamorphic Complex; LT Cerro La Torre; PR Paso del Rey; LA Loma Alta.
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1. INTRODUCCION
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The relationships between granites and consanguineous rare-element pegmatites of the
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petrogenetic LCT (Li-Cs-Ta) family of Černý and Ercit (2005) are many times obscured
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because they are usually found in different levels of the crust, and the erosion in little
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opportunities favors the observation of all of them in the same parental system. When the
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exposure allowed the observation, as it occurs in some places as Ghost Lake (Breaks and
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Moore, 1992), Harney Peak, Black Hills (Shearer et al., 1992) or Central Iberian zone
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(Roda-Robles et al., 2018), it is possible to establish a linkage that relates granites and
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pegmatites. In other districts, the integrated geological observations led researchers as
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Heinrich (1953) and Varlamoff (1972) to set patterns of regional zoning sketched by
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Trueman and Černý (1982), Černý (1991b) or London (2008). In these cases, the
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representativeness of the different kinds of pegmatites hardly reaches the ideal of the
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theoretical schemes. However, we think that this regional zoning represents the
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modifications produced throughout the process of fractional crystallization of the parental
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granites and the pegmatites and their description contributes to support the experimental
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results and helps to interpret the origin of these singular igneous rocks.
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In this paper we address the review of a pegmatite district that evolved in the western
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margin of Gondwana, which has the advantage of being located in a slightly tilted basement
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block that allowed the examination of the processes that happened in the upper part of the
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middle continental crust involving a thick sedimentary prism during an Eopaleozoic
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terrane-continent collision. The textures and the modal and chemical composition of the
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fertile granites are described and considered together with the main characteristics and
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distribution of the associated rare element pegmatites and the reasons of their metallogenic
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potential in lithium and tantalum mineralization. Previous studies about the district address
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the mineralogy and distribution of the pegmatites (Oyarzábal, 2004), the geochemistry of
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their K-feldspar and muscovites (Oyarzábal et al., 2009) and the age and origin of the
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associated granites (Steenken et al., 2006; López de Luchi et al., 2007). There is profuse
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complementary information background that tackle related specific points contributing to
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the understanding of the evolution of the district that will be quoted in due course.
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2. METHODOLOGY
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The cartography of the TPD was made with aerial photographs 1:20000 and planialtimetric
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restitution. Data collected and mapping of the main granitic pegmatites and description of
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the internal zonation was performed at different times always using the nomenclature
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established by Cameron et al. (1949) and Černý (1982). After inspection and description of
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the polished thin sections of medium grained granites and metamorphics, the modal
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compositions of leucogranites was obtained with a manual point counter using not less than
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1200 points per thin section. The modal count of the coarse- and pegmatitic-grained
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leucogranites was made on representative outcrops in the field and it is less precise that the one
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made in medium-grained facies under the microscope. The classification of the rocks was
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based in the IUGS system (Le Bas and Streckeisen, 1991) and the abbreviations of the
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minerals are after Whitney and Evans (2010). Major-, trace- and REE-analyses of whole
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rock powdered samples were done in Activation Laboratories Ltd. at Ancaster (Ontario).
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Sample digestion was done on Li-metaborate–tetraborate fused discs dissolved in weak
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nitric acid. Analyses were performed by ICP spectrometry (major elements) and ICP-MS
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(trace and REE). The detection limits for major elements were 0.01%, except for TiO2 and
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MnO (0.001%); for the following trace elements the detection limits were: Sc, Be, Co, Ga,
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Ge, Nb, Sn and W = 1 ppm; V, As and Pb = 5 ppm; Cr and Ni = 20 ppm; Cu = 10 ppm; Zn
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= 30 ppm; Rb, Sr, Y and Mo = 2 ppm; Zr = 4 ppm; Ag, Sb and Cs = 0.5 ppm; In and Hf =
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0.2 ppm; Ba = 3 ppm; La, Ce, Nd, Sm, Gd, Tb, Dy, Ho, Er, Yb, Ta, Tl, Th and U = 0.1
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ppm; Pr, Eu and Tm = 0.05 ppm; Lu = 0.04 ppm and Bi = 0.4 ppm.
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3. GEOLOGICAL SETTING
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The Totoral pegmatitic district (TPD) is located in the southwestern part of the San Luis range
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(Fig. 1A) that forms part of the Eastern Pampean Ranges. This range is a key location for
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understanding the geological processes occurring in the southwestern proto-margin of
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Gondwana, situation that has promoted in the past twenty years an increment in the research of
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the crystalline basement (see Morosini et al., 2017 and references therein). However, the rare-
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element granitic pegmatites are comparatively less studied even though they constitute most of
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the mineral resources that are being exploited in the area (Galliski, 1994a, b). The crystalline
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basement of the range was subdivided in three different NNE-SSW major elongated units that,
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from east to west, were named Conlara Metamorphic Complex (CMC), Pringles Metamorphic
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Complex (PMC) and Nogolí Metamorphic Complex (NMC) (Sims et al., 1997, 1998). The
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contact between these blocks is tectonic along ductile shear zones. The provenance studies
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(Steenken et al., 2004; Drobe et al., 2009) establish the differences among these units, and
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places the tectonic setting of sedimentation preferably in an active margin. They consider that
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the Th enriched metapsamites of PMC point to more felsic sources than the others, suggesting
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inputs from a recycled passive margin mixed with new felsic material. The PMC clastic
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sequence was sedimented in the western border of Gondwana from materials derived possibly
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from the Pampean orogeny or the Dom Feliciano/Gariep orogen (Drobe et al., 2009) during the
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Cambrian. The PMC was strongly folded developing a main penetrative foliation with NNE
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strike during the Famatinian orogeny. The PMC exposed sequence grades in a distance of
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approximately18 km from granulite facies locally developed in the contact with a belt of small
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mafic-ultramafic intrusives in the west, to amphibolite and greenschist facies eastward. The
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main lithologies comprise migmatites, gneisses, scarce amphibolites, mica schists with
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metaquartzites intercalations, phyllites and slates with minor intercalation of
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metaconglomerates (Perón Orrillo and Rivarola, 2014) arranged in NNE-SSW trending belts.
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According to Hauzenberger et al. (2001), the granulite facies with a paragenesis of Grt-Crd-Sil-
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Bt-Kfs-Pl-Qz-Rt±Opx reached PT conditions of 740-790ºC and 570-640 MPa during the
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M2(G) metamorphism. The migmatites, showing evidences of in situ melting, occur to the east
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of the granulites and grade eastward to gneisses. The paragenesis in this facies shows St-Grt-
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Bt-Ms-Pl-Qz-Ilm±Fi±Chl with peak conditions of 570-600ºC, 500-570 MPa reached during the
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M1(A) metamorphism (Hauzenberger et al., 2001). In the contact between the high and
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medium grade rocks, mylonites of the La Arenilla shear zone retrograde the granulite
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paragenesis to the amphibolite ones. The gneisses are in tectonic contact (sensu Sims et al.,
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1997; von Gosen, 1998; Ortiz-Suárez and Casquet, 2005) or grade (Ortiz-Suárez et al., 1992;
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Steenken et al., 2011) to a belt of mica schists that passes eastward to phyllites, ending with
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slates before the metamorphic grade increases again prior to the tectonic contact with the CMC.
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The mica schists were distinguished as a unit with this name (von Gosen, 1998) and they have
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tectonic boundaries with the phyllites and slates that were named San Luis Formation (Prozzi
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and Ramos, 1988). Sims et al. (1997), based in the different degree of deformation of the PMC
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and the San Luis Formation, considered that the late would be younger, and they mark the
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contact between the two units as a shear zone. However, detailed structural studies showed that,
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even though in several profiles there are reverse faults (von Gosen, 1998), possibly much of
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metasedimentary lithological units of the PMC and particularly the mica schists and the
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phyllites constitute, with structural discontinuities, a single crustal sequence and they will be
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considered as such (von Gosen, 1998; Steenken et al., 2006). The age of the M1 metamorphism
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was initially bracketed between 484±7 Ma and 451±10 Ma (Table 1, cf. Sims et al., 1998;
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Steenken et al., 2011 and references therein). However, recently Ferracutti et al., 2017 obtained
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two Nd-Sm isochrons that give 1289 (±97) and 1002 (±150) Ma for the high grade metaclastics
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and the ultramafic rocks respectively, that could indicate that in the western part of the PMC
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the outcrops of high grade rocks would be part of an older crystalline basement attributable to
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the lower crust.
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In the easternmost section of the mica schist belt, I- and S-type granites are emplaced, mostly
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arranged in the same NNE-SSW trend. The I-type granites are represented by the Pampa del
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Tamboreo granodiorite, dated by SHRIMP U-Pb in zircon at 470±5 Ma, that shows its western
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border affected by tectonism and the eastern side develops contact metamorphism in the San
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Luis Formation (Sims et al., 1997). In the studied area, the S-type granites form two main
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stocks named Cerro La Torre (LT) and Paso del Rey (PR) and a swarm of leucogranitic sills,
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dykes, pegmatites, and aplites distributed asymmetrically, mostly in the eastern flank of the
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granites (Galliski, 1994a). Sato et al. (2003) included them in their synorogenic granitoids
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respect to the Famatinian orogenesis. López de Luchi et al. (2007) studied some of these
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plutons grouped in their OGGS (Ordovician Granodiorite-Granite Suite) in the scope of the
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petrogenesis of the Paleozoic granitic rocks from the San Luis range. They subdivided the
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OGGS in high-T and low-T granites and proposed for the latter an origin based in biotite
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dehydration melting at low pressures of metagreywacke rocks, leaving plagioclase in the
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residue. The granites and pegmatite swarms show structural evidences of crystallization under
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a protracted compressive tectonic regime during the collisional Famatinian orogeny (ca. 500-
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440 Ma) that accreted, in a first episode, the Famatina Terrane to the Gondwana (Ramos,
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2010). Geochronology of the granites varies depending of the used method (Table 1). Llambías
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et al. (1991) dated by Rb-Sr isochron the Paso del Rey - Río de la Carpa granites in 454±21 Ma
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with 87Sr/86Sri of 0.712. Varela et al. (1994) obtained biotite ages from 372 to 391 Ma. Von
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Gosen et al. (2002) got a U-Pb zircon TIMS age of 608+26-25 Ma. Stenkeen et al. (2006)
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obtained a 207Pb/206Pb zircon evaporation ages of 597±54 and 491±19 Ma, meanwhile Stenkeen
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et al. (2006) dating by SHRIMP U-Pb the zircons of Paso del Rey north pluton obtained an
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upper intercept with the concordia at 456±30 Ma (MSWD = 0.26). In any case, the uncertainty
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produced by inherited zircons makes the determination of the crystallization age difficult. Since
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that the pegmatites associated with the Paso del Rey leucogranite intrude the granodiorite in
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Pampa del Tamboreo, the leucogranite data older than 470± 5 Ma have little confidence.
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Because of that, based on coincidence between the Rb-Sr isochron and the U-Pb age of
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Steenken et al. (2006), the probable age of the Paso del Rey leucogranite is considered ≈ 455±5
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Ma. The K-Ar biotite data of Varela et al. (1994) at 372 to 391 Ma are interpreted as the
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definitive cooling ages of the intrusive.
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4. THE S-TYPE LEUCOGRANITES
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4.1 Petrography
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The granites of the TPD form two irregular bodies named Cerro La Torre (LT) and Paso del
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Rey (PR) (Fig. 1B). Both are part of a larger S-type granite suite that also includes the
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Cerros Largos, La Florida and to the east, outside the studied area, the Río de la Carpa and
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Río Quinto plutons. Because most of the rare-element pegmatites are spatially associated
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with the PR and LT leucogranites, our study is heavily concentrated on them. To the south,
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the La Florida stock was studied by Carol et al. (2007) meanwhile Llambías et al. (1996)
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described the granitic rocks located to the north and east of the TPD. López de Luchi et al.
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(2007) consider samples of PR pluton in their low-T OGGS granites mentioned above.
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The LT granite is a small intrusive, built up by a few hundreds of lenses, sills and dikes that
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include deformed septa of metamorphics and has a few different petrographic variations. Its
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intrusion produced a partial metamorphic overprint in the hosting micaschist, which develops
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nodules of cordierite or muscovite -locally with fibrolite-, garnet and widespread
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tourmalinization. The two common petrographic types in the lenses are a light grey medium-
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grained rock (Fig. 2A) and a light-pink pegmatitic-grained rock (Fig. 2B). The medium-grained
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granite is formed by quartz (3-1 mm), plagioclase (An13-16) with bent twin planes, microcline (<
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5mm), and bent muscovite as the main accessory mineral. Garnet occurs in 1-2 mm euhedral
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grains and tourmaline is associated with late-stage quartz crystals. Biotite is present in the
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southern part of the leucogranite replaced by muscovite. In the contact with the metamorphics
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the grain size diminishes and euhedral crystals of muscovite are parallel to the schistosity. The
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pegmatitic facies form irregular lenses and areas with transitional borders. They are composed
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by coarse (20-30 cm) subhedral microcline crystals contained in a groundmass mostly formed
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by quartz and coarse-grained (up to 15 cm) muscovite with feathery habit. The most common
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accessory minerals are schorl in 5-7 cm sized crystals, garnet and, less frequently, anhedral
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apatite-supergroup minerals and monazite. Occasionally microcline is concentrated forming
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almost monomineralic meter-sized irregular domains. Albitization affects both facies
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developing, in irregular sectors, pervasive replacement formed by an assemblage of Ab-Qz
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(≈90%)-Ms±Grt-Ap-Tur. Albite (An4-8) shows up to 10 mm crystals with undulose extinction and
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bending, suggesting synkinematic crystallization. Late-stage quartz-feathery muscovite rich veins
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with schorl, apatite and Mn-Fe oxides fill joints in the NW part of the stock. In the central and
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southern parts of the intrusive there are frequent subspherical pods of pegmatitic differentiates up
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to 1 m diameter that contain euhedral crystals of garnet, schorl and muscovite. The finer- (Fig.
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3A, 3B) and pegmatitic-grained rocks have modes (Table 2) corresponding to monzogranite-
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granodiorite and alkalifeldspatic granite, respectively (Fig. 4). To the northeast of the LT
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leucogranite, the outcrops of pegmatitic leucogranite become more sporadic and form sub
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parallel lenses up to a hundred meter wide in the thicker parts, which are intruded and
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harmonically folded in the mica schists without evidences of associated rare-element
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pegmatites.
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The PR is a larger stock, of general ovoidal geometry with the main axis oriented N15-35ºE,
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and formed by irregular and major separated outcrops (Fig. 1B) composed by three different
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facies. To the east of the leucogranites, in the surroundings of San Luis pegmatite, the host
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rocks are composed by mica schists with phenoblasts of muscovite, garnet and staurolite
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contained in a groundmass of Ms-Qz-Bt-Chl-Pl±Ap-Tur-Zrn-Hem. The main rock of the PR
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pluton forms thick lenses (Fig. 2C) of light-gray to pinkish, medium-grained monzogranite
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composed of Qz+Kfs+Pl+Ms-Bt±Tur±Gr±Ap±Zrn±Mnz±(Sil). Quartz forms anhedral grains
235
with undulose or fragmented extinction and myrmekitic intergrowths with plagioclase.
236
Plagioclase (An12-24) occurs as subhedral, frequently bended, weakly zoned crystals. Microcline
237
occurs as interstitial, late-stage, anhedral crystals that usually include the other phases, mostly
238
quartz in optical continuity. Perthite intergrowths are infrequent. Muscovite forms up to 15 mm
239
subhedral crystals, commonly bent, that occasionally include euhedral biotite. Locally, near the
240
contact with the host rock, the muscovite and biotite contents increase and both minerals show
241
subparallel orientation giving a very slight foliation. Tourmaline is present in the same areas
242
where muscovite is abundant, in 1-2 cm prismatic crystals; garnet is usually irregularly
243
associated with tourmaline or biotite in euhedral crystals and sometimes intergrown with
244
apatite (Fig. 3A, B). Zircon and monazite crystals are scarce. The sample M49 was taken 850
245
m to the NW of the PR leucogranite in the western lens that crops out on the road La Arenilla -
246
Paso del Rey. It is a different finer-grained leucogranite, foliated, garnet-bearing, and with
247
lenses of sillimanite (fibrolite), disconnected from the PR main lenses. Fibrolite is also present
248
in the northern part of the PR leucogranite and in the outcrops of some Loma Alta (LA) sills
249
forming subparallel aggregates frequently associated with muscovite. Modal counts show that
250
all the rocks are monzogranites and that in its central area the intrusive has higher Kfs/Pl ratios
251
(Table 2, Fig. 4). Several types of quartz bearing or pegmatitic zoned dykes, up to one meter
252
wide and mostly subparallel to the main axis of the intrusive were described and considered
253
cogenetic with the PR granite (Oyarzábal and Galliski, 1993).
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In the central and southern parts of the PR intrusive, a very coarse-grained to pegmatitic
255
leucogranite that transitionally passes to the medium grained monzogranite is volumetrically
256
significant. This rock is formed by cm to m-sized perthitic K-feldspar megacrysts, occasionally
257
including micrographic quartz, included in a Qz-Ms-Ab±Tur-Grt-Ap groundmass. Quartz
258
forms milky to pink masses containing the other minerals. Muscovite occurs in two
259
generations: as up to 15 cm books included in quartz or K-feldspar, and including schorl, or as
260
small flakes pervasively replacing feldspars. Garnet occurs in 5-7 cm euhedral crystals usually
261
immersed in quartz. Plagioclase is subordinate replacing K-feldspar with cleavelandite or
262
sugary habit.
263
In the eastern flank of the PR intrusive outcrop many lenses (<160 m thick, ~500 m length) of
264
pegmatitic leucogranite separated from the main granite by decametric septa of schists. This is
265
a light gray with pinkish hue rock with megacrysts of perthitic K-feldspar (Fig. 2D), sometimes
266
showing graphic texture, contained in a medium grained groundmass composed of Qz-Pl-Kfs-
267
Ms±Tur-Grt-Ap. Close to the contact with the hosting mica schists occur small schlierens
268
formed by tourmaline, biotite and garnet.
269
Between the LT and the PR leucogranitic stocks occurs a dome, with its main axis oriented NE-
270
SW known as LA. It is formed by many sills of pegmatitic leucogranites intercalated in the Bt-
271
Ms- schists. The mica schists are crosscut by Qz-Pl-Ms cm wide veins with fibrous sillimanite
272
growing in muscovite or in the interphase quartz-plagioclase. The eastern flank of the LA high
273
is the most heavily populated with lenses of pegmatitic leucogranite usually concordant with
274
the schistosity of the folded host rocks. For comparison with other uplift situated to the east
275
(e.g., Río de la Carpa leucogranite), these dome structures occur in the upper part of the
276
leucogranite stocks.
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Comparing with other localities, the mineral composition and textures of the LT described
278
rocks fit well with the muscovite-tourmaline leucogranites from the Harney Peak, South
279
Dakota (Norton and Redden, 1990), or High Himalaya leucogranites (e.g., Scaillet et al., 1990;
280
Visonà and Lombardo, 2002), meanwhile the PR stock is built by muscovite-tourmaline and
281
also muscovite-biotite leucogranites.
282
4.2 Geochemistry
283
A considerable fraction of the rocks that conform the TPD leucogranites are very coarse grained
284
to pegmatitic textured and introduce the problem on the representativeness of the samples. For
285
this reason, the whole-rock chemical analyses were performed only on medium to coarse-
286
grained facies. Pegmatitic facies were investigated based in some major and trace elements of
287
K-feldspar and muscovite (Oyarzábal et al., 2009). Table 3 displays the geochemical data for
288
samples of the LT and PR leucogranites and metamorphics from the PMC. With the exception
289
of sample LT25 the samples from LT and PR stocks have silica contents of 73.36 to 73.74 wt.%
290
SiO2 (avg. for both stocks, respectively), high alumina (14.96, 14.18 wt.% Al2O3), low values of
291
TiO2 (0.04, 0.04 wt.%), MgO (0.12, 0.17 wt.%), CaO (0.59, 0.67 wt.%), FeOT (0.65, 0.58
292
wt.%) and MnO (0.08, 0.12 wt.%). The average contents of Na2O is 3.97, 3.59 wt.% and of
293
K2O 4.55, 4.47 wt.% respectively. The average molar ratio of the granites show K/(K+Na) =
294
0.42, 0.45, and the average trace elements contents (ppm) of Ba 331, 190; Rb 124, 189, and Sr
295
83, 51 respectively. The Rb/Sr ratios are 0.5-4.4 and 2.1-5.5 for LT and PR plutons. These
296
rocks are high silica, strongly peraluminous granites with average ASI (Alumina Saturation
297
Index = Al/(Ca-1.67P+Na+K) values of 1.20 and 1.22 for LT and PR stocks, respectively. The
298
high ASI values and low Mg+Fe contents (Fig. 5) plot these rocks in the field of collisional
299
leucogranites (Nabelek and Liu, 2004). Among the four different types of rare-element granites
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recognized by Linnen and Cuney (2004) and Černý et al. (2005), the TPD leucogranites have
301
SiO2/P2O5 and Th/Zr ratios similar to their peraluminous intermediate phosphorous rare-
302
element granites (Fig. 6A, B).
303
The content of REE is overall low, with average ΣREE of 18.5 and 26.9 ppm for rocks of both
304
stocks, most of which are slightly LREE enriched (14.7 and 21.4 ppm, respectively). The Eu
305
negative anomaly is weak in three samples of LT (Eu/Eu* 0.4-0.7); the remaining samples have
306
positive anomaly up to 4.7 Eu/Eu*. Meanwhile, most of the PR rocks have moderate Eu
307
negative anomalies (Eu/Eu* 0.4-0.9) with one sample without it (Eu/Eu* 1). The chondrite
308
normalized patterns (Fig. 7A) are similar to the biotite-muscovite, and tourmaline leucogranites
309
from Harney Peak (Duke et al. 1992, Nabelek and Liu, 2004), with the difference of
310
enrichment in LREE and HREE in TPD samples. Figure 7A also shows the REE plots of the
311
three more characteristic samples of the PMC which are very similar to the average metapelites
312
composition from Zanskar, Himalaya (Ayres and Harris, 1997). We interpret that the weak
313
enrichment of TPD leucogranites in LREE and HREE is possibly due to the contents of
314
monazite (±apatite) and garnet (± zircon), respectively. The few europium positive anomalies,
315
not rare in pegmatitic layers of leucogranites as Calamity Peak (Harney Peak, South Dakota)
316
has been suggested that can be originated by that feldspar (1) were not important in the
317
fractionation process, (2) were may be locally accumulated or (3) the f(O2) may have increased
318
(Duke et al. 1992). The spider diagram (Fig. 7B) shows compared with peraluminous
319
intermediate phosphorous rare-element granites, a similar pattern with peaks slightly less
320
marked but showing similar behavior for Th, Ta, Ti and REEs.
321
We used the Zr and REEs contents of the leucogranites to calculate the temperature based in
322
the zircon saturation thermometry (TZr) of Watson and Harrison (1983) and LREE saturation
323
thermometry (TREE) proposed by Montel (1993). The results (Table 3) show values ranging
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from TZr 640-725 ºC for LT and 642-713 ºC for PR. The TREE gives values comprised between
325
603 and 698 ºC for LT and 621 to 727 ºC for PR. The results are plotted in the diagram of
326
Figure 8. The lowest temperatures correspond to TREE of samples LT07 (604 ºC) and M49
327
(621ºC) and are considered too low. Both are from thick leucogranitic lenses situated in the
328
NW direction away of the main plutons in PR and LT respectively.
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329
5. GEOLOGY AND TYPES OF THE RARE-ELEMENT PEGMATITES
331
The pegmatites of the TPD are distributed in three groups located mainly in the eastern
332
flank of the described granitic rocks which are known as Cerro La Torre, Loma Alta and
333
Paso del Rey pegmatitic groups (Oyarzábal et al., 2009). They coexist spatially with sills
334
and dykes of pegmatitic leucogranites. The criteria used to differentiate rare-element
335
pegmatites from pegmatitic leucogranites in this pegmatitic district attend basically to the
336
different internal zoning and accessory mineralogy of both kinds of rocks. Pegmatites have
337
relatively well developed zoning of the different internal units, coarser grain size and
338
discrete to significant presence of accessory rare-element minerals. Instead, pegmatitic
339
leucogranites lack of very well developed zoning, especially the quartz core zone, have
340
traces or scarce, if any, accessory rare-element minerals and the grain size is usually
341
smaller. They are similar to the simple pegmatites of Norton and Redden (1990) or London
342
(2008). Rare-element pegmatites are volumetrically very subordinate to pegmatitic
343
leucogranites, possibly less than 3% (see Fig. 1B), which is perfectly embraced in the
344
standards for other pegmatite fields as Harney Peak (≈ 2%, Norton and Redden, 1990). The
345
most important pegmatite bodies that were intermittently mined in the past for beryl,
346
tantalite, muscovite, K-feldspar, albite, quartz or a variable combination of them are quoted
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in the Table 4. These pegmatites have been classified in types and subtypes of the rare-
348
element class, following the systematic of Černý and Ercit (2005), based mainly in internal
349
structure, bulk composition, rock-forming and accessory minerals and geochemical
350
signature. The main types of pegmatites are: (1) barren-transitional to beryl type
351
pegmatites: e.g., La Vistosa (I, II, III, IV and V); (2) beryl type, beryl-columbite-phosphate
352
subtype pegmatites: e.g., Santa Ana, La Empleada, Los Aleros, Los Chilenitos, Ranquel
353
and Cacique Canchuleta; (3) complex type, spodumene subtype: San Luis II, Víctor Hugo;
354
(4) albite-spodumene type: San Luis I, La Teresaida (with some features of spodumene
355
subtype), Diana and Cargil, and (5) albite type: Independencia Argentina and Aquelarre
356
with Los Chilenitos, La Argentina and La Rioja sharing some characteristics. In terms of
357
economic rare-element mineralization these different types of pegmatites could be named
358
as barren (1), beryl-bearing (2), lithium-bearing (±Nb-Ta) (3, 4), and Nb-Ta albite-bearing
359
(5) pegmatites. All the pegmatites have, to a different degree, internal zoning.
360
The barren-transitional to beryl type pegmatites of the LA pegmatite group are hosted into
361
leucogranitic lenses (La Vistosa I) or mica schists. The emplacement has been in few cases
362
permissive to, mainly, forceful, with strong structural control by a sub-parallel joint pattern.
363
The largest pegmatite dyke is 12 m wide and 105 m long. All pegmatites are poorly zoned,
364
with a variable mineral composition that is: border (Qz-Ms-Pl±Grt), wall (Mc-Qz-Ab-
365
Ms>Bt±Tur-Grt-Ap), intermediate (Mc-Qz-Ms-Ab±Tur) and core (Qz±Brl) zones; some of
366
them have scarce beryl and <5 cm altered Mn-Fe phosphates (Colaianni and Oyarzábal,
367
2008).
368
The beryl-columbite-phosphate subtype of beryl type pegmatites are located in the
369
southeastern part of the LT granite, and at the southeastern area of the LA Group. The
370
pegmatite outcrops are 60-90 m long and less than 30 m wide, and occur as single tabular to
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lenticular bodies intruding with sharp contacts the mica schists. In the surroundings of
372
Santa Ana pegmatite the bodies are folded and segmented. They are moderately to well
373
zoned, showing the following units: border, wall, intermediate and core (Qz±Brl) zones.
374
The primary mineral association comprises Qz-Mc-Ab-Ms-Brl-Col-Tur-Ap-Grt. Huge
375
crystals of Kfs (La Empleada, Fig. 9A), or discrete (Santa Ana) to giant (Ranquel, Fig. 9B)
376
nodules of primary phosphate minerals of the triphylite-litiophilite or beusite-graftonite
377
series occur in the core-margin association. It is characteristic of the TPD, and even of the
378
Conlara pegmatite district to the north, the Mn >> Fe geochemical signature of the primary
379
phosphates. Exsolution (Hurlbut and Aristarain, 1968; Hatert et al., 2012), magmatic
380
replacement (Galliski et al., 2009) or hydrothermal reworking of these primary phases
381
originate interesting associations of Mn-Fe-(Al-Ca-Li) mineral phosphates as qingheiite,
382
zavalíaite, huréaulite, etc. Mining of these kinds of pegmatites was drifting from beryl in
383
the 50´ and 60´ of the last century to muscovite, feldspar and quartz of ceramic grade in
384
recent times.
385
The albite-spodumene type pegmatites occur in the southernmost part of the TPD emplaced
386
in mica-schists nearby the pegmatitic facies of the PR leucogranite. They have tabular
387
shape with high aspect ratio. The modal composition shows albite and quartz dominant
388
over spodumene and K-feldspar, and a homogeneous and symmetric internal structure, with
389
a dominant internal zone of microcline and spodumene crystals enclosed in a medium-
390
grained Ab-Qz-Spd±Ms-Ap-Grt groundmass. The prismatic microcline and spodumene
391
crystals display parallel orientation forming comb-structure approximately normal to the
392
strike of the pegmatite (San Luis I pegmatite, Fig. 9C). San Luis I and La Teresaida
393
pegmatites have been synkinematically intruded and folded during their emplacement
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showing usually straining and stretching along the strike and occasionally some incipient
395
development of the quartz core (La Teresaida).
396
The complex type, spodumene subtypes pegmatites are San Luis II and Víctor Hugo. San
397
Luis II is located in the core of some anticlinal crests of a folded albite-spodumene type
398
pegmatite, named San Luis I (Oyarzábal and Galliski, 1993). The internal structure is
399
complex, consisting of border (Ms-Qz±Bt-Grt-Ap), wall (Mc-Qz-Ms-Spd), intermediate
400
(Mc-Qz-Spd±Ms-Ab) and core (Qz) zones; spodumene forms giant prismatic crystals (~ 2
401
m long in San Luis II) hosted in the massive quartz of the core. Accessory triphylite-
402
lithiophilite in discrete nodules sometimes altered to mitridatite (Galliski et al., 1998) and
403
Ms-Ab replacement units contain tantalite-(Mn) as accessory minerals or scarce cassiterite,
404
as in Víctor Hugo pegmatite (Galliski and Černý, 2006). Most of the Li-bearing pegmatites
405
were mined for spodumene and presently are being explored for their lithium resources.
406
The albite type pegmatites are located in the southeastern area of the LT and in the northern
407
part of the PR groups. The most typical are Independencia Argentina (Galliski et al., 2015)
408
and Aquelarre, but Los Chilenitos, La Argentina, and La Rioja show intermediate features
409
between beryl and albite type pegmatites. They are tabular bodies, approximately 200 m
410
long and 5-20 m wide, emplaced in quartz-mica schists, with N35º-40ºE strike and 45º-
411
70ºW dip. Zoning is asymmetric, with border (Ab-Qz±Ms-Ap), wall (Qz-Ab), outer
412
intermediate (Ab-Qz±Ms), middle intermediate (Ab-Qz-Spd±Ms), inner intermediate (Ms-
413
Qz±Ab) and core (Qz±Ms) zones, and a fine-grained Ab-bearing replacement unit (Ab±Qz-
414
Ms-Ap-Col) (Fig. 9D). These pegmatites were mined for beryl, columbite, fine-grained
415
muscovite and albite.
416
The chemical composition of the columbite-group minerals show variations related to the
417
type of pegmatite (Fig.10). In general, pegmatites of complex type, spodumene subtype
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418
show the most evolved chemical trends towards increasing #Ta and #Mn. Albite-type
419
pegmatites have moderately evolved CGM that show rhythmic zoning.
420
6. DISCUSSION
422
6.1 Source and origin of the S-type leucogranites
423
The high ASI values and low Mg+Fe contents (Fig. 5) of TPD granitic rocks is particular of
424
collisional leucogranites showing the two different petrographic types: tourmaline-muscovite
425
and biotite-muscovite, common in other occurrences (e.g., Scaillet et al., 1990; Nabelek and
426
Liu, 2004). These properties as well as the high 87Sr/86Sri relationships of 0.712 (Llambías et al.,
427
1991), the trace element contents (Table 3), the REE pattern (Fig. 7), and the values of TZr and
428
TREER (Fig. 8) of the LT and PR rocks are typical of S-type leucogranites (London, 2008) and
429
approximately in the range of leucogranites elsewhere as Manaslú, Everest, Gangotri or
430
Yadong, Himalaya (e.g., Montel, 1993; Visonà and Lombardo, 2002; Gou et al., 2016).
431
As in other occurrences, these leucogranites are generated belatedly during compressional
432
deformation and metamorphism of the metasedimentary prism in the upper plate of the
433
collisional orogeny (Nabelek and Liu, 2004 and references therein). Most authors consider,
434
based on isotopic data, that the source rock is located in the lower levels of the same unit
435
that they intrude (e.g., Deniel et al., 1987; Patiño-Douce and Harris, 1998) without influx
436
from other sources (Hopkinson et al., 2017). This interpretation suggests that probably the
437
dominant source of the TPD granites are the metapelites (±metagreywackes) of the PMC,
438
which show macroscopic evidences of partial melting in the migmatites (this paper) at P-T
439
conditions up of 570-600 ºC, 500-570 MPa determined by Hauzenberger et al. (2001) in the
440
amphibolite facies, or 790 ºC -720 MPa in the paragneisses (Ortiz-Suárez and Casquet,
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2005). The LT, PR and similar leucogranites are built by addition of lenses, sills (Fig. 2C)
442
or laccoliths formed by the intrusion of episodic batches of melts (Harrison et al., 1999),
443
transferred from the source by shear zone systems (Brown and Solar, 1998; Solar et al.,
444
1998), that imprint some local thermic metamorphism to the host rocks. The origin of the
445
melts is adscribed to incongruent melting of the protoliths in disequilibrium conditions
446
(Harris et al., 1995). Their bimodal petrography, with muscovite-tourmaline and biotite-
447
muscovite facies (Guillot and Le Fort, 1995; Visonà and Lombardo, 2002), reflects their
448
origin and has been preferably attributed to low pressure (500-1000 MPa) fluid-absent
449
muscovite dehydration melting of metapelites the first, and to biotite dehydration melting
450
of metapelites or metagraywackes the second (see Nabelek and Liu, 2004). Dehydration
451
melting is the preferred origin because in fluid-present melting the resulting melts are of
452
trondhjemitic composition (Patiño-Douce and Harris, 1998). Besides, most of the Rb/Sr
453
values of the LA and PR are 2-5 higher than those produced by water-saturated melting
454
(Harris and Inger, 1992). At low pressures (400 to ≈ 1000 MPa) the muscovite dehydration
455
melting is produced at lower temperatures than biotite dehydration melting. Weighing the
456
mineral and chemical composition of the LT and PR leucogranites, we note that biotite is
457
almost absent in the first, and locally present in small quantity in the second. The calculated
458
temperatures (Table 3, Fig. 8) and the Ba vs Pb contents (Fig. 11) also indicate that LT is a
459
low-T S-type leucogranite according to Finger and Schiller (2012) and that PR shows
460
higher temperature of generation. Based on these attributes we interpret that the LT
461
leucogranite was produced dominantly by muscovite dehydration melting of the PMC
462
metapelites and the PR was produced by muscovite plus incipient biotite dehydration
463
melting of PMC metapelites and metagraywackes. The chemical composition of both, and
464
their metallogenic potential, is related to the mineral composition of the source and the
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mechanism of melting. Muscovite dehydration melting consumes muscovite, plagioclase
466
and tourmaline from the pelitic mica schists, leaving some monazite, possibly armoured in
467
biotite, in the restitic fraction which produce the REEs low contents, the flat profiles (Fig.
468
7, Nabelek and Bartlett, 1998), and yields a small volume of melt which is in agreement
469
with the size of the LT stock. The B, Rb, Cs, low Li and Ta, and variably Be content of the
470
rocks is provided by muscovite and tourmaline and impart the LCT signature to the melts
471
(Icenhower and London, 1995, 1996; Evensen and London, 2003; London, 2008). In the
472
case of biotite dehydration melting, the temperature is higher, the melt volume increases, as
473
well as the quantity of Li-Cs-Ta contained in both biotite and muscovite, and other trace
474
elements producing increasing rare-element fertility. Melting of biotite also produces
475
higher contents of transition elements that generates biotite in the crystallizing leucogranite,
476
constrained to a low or moderate B content (Nabelek et al., 1992; Guillot and Le Fort,
477
1995). Both processes of melting are frequently in disequilibrium and the melts generally
478
contain entrained crystals of zircon and occasional monazite which complicate the U-Pb
479
dating giving older ages (Harrison et al., 1999). Mayor fractionation of S-type melts as an
480
alternative model for the origin of leucogranite (e.g., Scaillet et al., 1990, 1995) is discarded
481
in TPD because grouped plots of mayor elements in Harker diagrams (not shown) and week
482
Eu anomalies in REEs diagram (Fig. 7A) precluded it. However, after emplacement, during
483
the crystallization of the leucogranites, crystal-melt fractionation was very active as shown
484
by the trace elements variation of the K-feldspars (Oyarzábal, 2004) and the dispersion of
485
LT data along the slope of the line that divides both leucogranite fields in Figure 11.
486
Regarding to the necessary heat for the generation of leucogranitic melts, Nabelek and Liu
487
(1999, 2004) evaluate and model some possibilities proposed by different authors as: (1)
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increment of geotherms in the “cold” upper plate of a thickened crust; (2) the same but in a
489
“hot” upper plate of a thickened crust; (3) decompression melting; (4) thinning of mantle
490
lithosphere; (5) shear heating. They favor the shear heating (or strain heating, see Nabelek
491
and Nabelek, 2014) as the mechanism that triggers the melting of the protolith,
492
predominantly of the overthrusted slab of the plate, in our case the PMC. This mechanism
493
should also explain why along the same belt of S-type leucogranites - LCT rare-element
494
pegmatites there are differences in the temperature of generation of the melts and in the
495
type of mineralization of the pegmatites between the northern Be-bearing LT and LA
496
groups, and the southern Li (Ta)-bearing PR group.
497
6.2 Genetic links between granites and pegmatites
498
The close location of the TPD pegmatites to the LT, LA and PR leucogranites is prima
499
facie suspect of some parental relationships. The distribution of the rare-element pegmatites
500
is clearly defining three groups located preferably in the eastern side of the leucogranites.
501
The pegmatites are forming an imperfect regional zoning focused in these three intrusive
502
centers, whose pattern follows the general scheme developed by several authors
503
(Varlamoff, 1955; Trueman and Černý, 1982; London, 2008), and became an additional
504
fact supporting the hypothesis of parental relationships.
505
Oyarzábal et al. (2009) studied the geochemistry of K-feldspars in the granites and
506
pegmatites of this district in order to check the variations in chemical composition along the
507
fractionation of the different kinds of pegmatites established by several authors in other
508
pegmatite districts (e.g., Gordiyenko, 1971, 1976; Černý, 1994), and following the range of
509
chemical variation sketched for the Pampean Pegmatite Province (Galliski et al., 1997).
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The results of the K/Cs versus Rb variation diagram (Fig. 12A) for example, shows a clear
511
fractionation trend from the Kfs of the leucogranite intrusives to the geochemically most
512
differentiated rare-element pegmatites of the albite type.
513
Likewise, the ages of granites and pegmatites are in good correlation (Table 1). The
514
mentioned Rb-Sr isochron of PR and Río de la Carpa leucogranites of 454 ± 21 Ma with
515
87
516
given by Steenken et al. (2008) for the PR stock are in agreement with the 450 +10-2 Ma
517
LA- ICPMS age for columbite from San Luis II pegmatite (von Quadt and Galliski, 2011),
518
the U-Pb chemical age of 460±15 Ma for uraninite from Santa Ana pegmatite (Linares,
519
1959), or the 444.5 ± 9.2 Ma obtained in muscovite from a pegmatite that cuts across the
520
PR leucogranite (López de Luchi et al., 2002). The older U-Pb zircon TIMS age of
521
608+26-25 Ma obtained by von Gosen et al. (2002) for the PR stock would be contaminated by
522
inherited zircons from the PMC protolith.
523
The excellent agreement between spatial relationships, geochemical fractionation trends
524
and ages points to a common origin of leucogranites, pegmatitic leucogranites and rare-
525
element pegmatites of the TPD as occur in other analogous systems worldwide (Černý,
526
1991b; Černý et al., 2005; Roda-Robles et al. 2018).
527
6.3 Conditions of emplacement and crystallization of the pegmatites
528
The temperature and pressure of emplacement and crystallization of the TPD rare-element
529
pegmatites vary depending of the type of pegmatite. The albite-spodumene type pegmatites
530
do not show petalite or squi (spodumene + quartz pseudomorphs after petalite) and this
531
limits their lower pressure of crystallization at the stability field of spodumene which is 600
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Sr/Sr86 ri ratios of 0.712 (Llambías et al., 1991) or the age of 456±30 Ma (MSWD 0.26)
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ºC at ≈ 350 MPa (London, 1984). This estimation is not discordant with the T-P data of
533
Ortiz Suárez and Casquet (2005) that is 594 ºC - 530 MPa for the peak metamorphism of
534
the mica schists and 550 ºC - 470 MPa for the fine grained mica schist in transit to
535
phyllites. The albite-spodumene pegmatites were emplaced in an open system and
536
crystallized synkinematically (Oyarzábal and Galliski, 1993) as the typical stress-related
537
textures show (Fig. 9C, Černý, 1991a). The beryl-type pegmatites were intruded and
538
crystallized in closed system being later deformed. The albite-type pegmatites were
539
intruded and crystallized mostly in a closed system sporadically opened for a new pulse or
540
degassing of volatiles (Galliski et al., 2015).
541
The regional zoning suggests that the trend of fractionation of the parental leucogranites is
542
reflected in the distribution of the different types of pegmatites in each group and, partially,
543
in the fractionation trends shown by the trace elements of the Kfs. This argument linked
544
with the timing of the relationship between crystallization-deformation gives the temporal
545
sequence of intrusion that would be: barren → beryl type → albite-spodumene type or
546
complex type spodumene subtype → albite type. It is clear from mapping that in this
547
direction diminishes the metamorphic grade of the host rock. Thus, the distance of intrusion
548
would be related to the interplay of temperature of the host rock with viscosity of the
549
pegmatitic melts, assuming that the emplacement was pressure-driven toward decreasing
550
isobars, as it seems that has happened in these LCT petrogenetic family of orogenic
551
pegmatites. The grain size of the leucogranites, pegmatitic leucogranites, and different
552
types of pegmatites also suggest that undercooling combined with the water content of the
553
melts were the key factor that controlled the observed textures, as is shown by experimental
554
works (Fenn, 1977; London, 1992, 2008, 2018; Webber et al., 1999; Baker and Freda,
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2001; Simmons and Webber, 2008; Nabelek et al., 2010; Sirbescu et al., 2017, Maneta and
556
Anderson, 2018).
557
6.4 Implication for the origin of the pegmatites
558
The rare-element pegmatites melts were generated by the long-lasting crystal-melt
559
fractionation process of the parental leucogranites, which happened in large individual
560
batches of melts or in the successive amalgamated batches of the episodic intrusions that
561
formed the incremental plutons. The pegmatitic melts enriched in alkalis, fluxes, and
562
incompatible elements, with lesser viscosity than the leucogranites, were intruded in the
563
hosting mica schists between 100 to 1000 m away in normal cases, or up to 2500 in albite-
564
type pegmatites.
565
The melt that produced the beryl-type pegmatites was more viscous than the corresponding
566
to the Li-bearing pegmatites and formed closer, thicker and shorter bodies with very coarse,
567
usually idiomorphic crystals of Kfs (Fig. 9A). They show higher contents of P in the Kfs
568
than other pegmatites (Fig. 12B) as well as giant nodules of primary Mn-Fe (Li)-
569
phosphates. These attributes suggest that in most of them it was active some residence time
570
in the crystallizing chamber, which could facilitate some immiscibility process that
571
concentrated P, Mn, Fe and Li in an exsolved phase. The very low contents of Mn, Mg and
572
Fe in the parental granites, insufficient to crystallize biotite in most of them and that drives
573
boron close to or inside the host rocks of the granites and pegmatites to form schorl,
574
contrast with the large nodules of Mn-Fe(±Li) phosphates, suggesting that some interaction
575
with mass-exchange of Mn-Fe(±Mg) between pegmatite melts and the micaceous host rock
576
could have been active.
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The Li-bearing pegmatites present in the PR group show that most of them crystallized
578
under dynamic conditions as evidenced by the typical UST (unidirectional solidification
579
textures) of the albite-spodumene type considered as synkinematic (Černý, 1991a). Their
580
origin is linked with three possibilities: (1) higher initial contents of Li of the PR
581
leucogranitic melts, (2) larger volume of the fractionated melt than in LT or LA
582
leucogranites, or (3) most protracted time of fractionation. It is possible that all these
583
factors had some influence but we prefer to stress the possibility that relates the higher Li
584
mineralization of the PR group to the increased participation of biotite during the
585
dehydration melting of the protolith, which would be caused by the higher temperature of
586
origin of its parental melts.
587
The extraction of the pegmatitic melts for reaching the regional zoning is still discussed
588
(Shearer et al., 1992, London 2008). A model of vertical zoning in the leucogranite
589
chamber with less viscous layers at the top that are extracted first, followed sequentially by
590
the less evolved melts, has been suggested for Iberian pegmatites (Roda-Robles et al., 2016,
591
2018). This model, useful to explain the links between pegmatites associated to large,
592
batholithic intrusions, finds some inconsistences when applied to the TPD. Some of them
593
are: (1) the leucogranites do not show differentiated rocks that support some type of vertical
594
zoning, (2) the pegmatites do not show fractionation along the strike, as it is frequent in
595
some pegmatites of Central Iberian zone (Roda-Robles et al., 2016), (3) the most evolved
596
pegmatites of albite-type show less deformation than the more primitives of beryl type. We
597
think that an alternative possible explanation for the regional pegmatite zoning of the TPD
598
is that they are the result of a process where different batches of leucogranites were the
599
parents of different pegmatites. The most feasible mechanism of extraction of the
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pegmatitic melts from the leucogranites would be by episodic tectonic squeezing. The
601
composition of the different pegmatitic melts should be conditioned by the degree of
602
fractionation of each batch at the time of extraction and its rare-element fertility. More
603
detailed precise geochronological work is necessary to demonstrate this possibility.
604
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6.5 Relationships between pegmatites and tectonics
606
The pegmatites of the TPD show evidences of deformation that happened during and after
607
emplacement. Some of the observed fabrics features are: folding, fractures, bending,
608
boudinage, stretching and strained textures. Folding is more developed in a long and
609
narrow belt situated eastward of the leucogranites that join La Teresaida, San Luis, La
610
Argentina, La Empleada and Santa Ana pegmatites. Some authors (Sims et al., 1997; von
611
Gosen 1998) mapped a non-linear shear zone separating mica schist and phyllites. This
612
zone is defined by deformed mica schists, stretched intercalated leucocratic veins and
613
truncated foliations. There are also minor faults, folded (e.g., San Luis, La Teresaida) and
614
locally fractured (La Teresaida, La Argentina, La Empleada) pegmatites that point to a
615
strained, non-linear belt that bounds the fine-grained mica schist with the phyllites.
616
It is known that there is a close temporal and spatial link between synkinematic granitic
617
plutons and shear zones (Hutton and Reavy, 1992). Shear zones control ascent and
618
emplacement of granitic magmas (Brown and Solar, 1998; Weinberg et al., 2004) and can
619
give rise to a number of low pressure sites, not only in pressure shadows around competent
620
rocks, but also in dilational jogs, pull-apart regions, shear zone terminations, or dilatational
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areas resulting from active, crosscutting shear zones (Weinberg et al., 2009 and references
622
therein).
623
The occurrence of pegmatites near and within the shear zone separating mica schists and
624
phyllites suggests a temporal and spatial link between both. Thus, the emplacement of
625
pegmatitic melts was possibly favored by low pressure sites developed along this ductile
626
shear zone.
627
The ductile strain of the belt, active during the emplacement of the pegmatites, was
628
possibly promoted by the rheological changes occurred in the conjunct mica schists -
629
pegmatites, produced by the heating contributed by pegmatitic intrusives, whose
630
emplacement was facilitated by the stress released in the shear zone. This would explain the
631
eastward asymmetry of the pegmatite distribution (towards the shear zone) and that the
632
emplacement occurred during the latest compressional events. Eastward of the mentioned
633
deformed belt, the folding vanishes and the pegmatites show softer evidences as boudinage,
634
stretching and internal deformation (Independencia Argentina, La Rioja). Some examples
635
of folding and fracturing (Fig. 9E, F) show that the emplacement was a synkinematic,
636
forceful, polypulsatory process that in extreme cases dismembered some zones of
637
crystallizing pegmatites. Galliski (1994b) suggested that the leucogranites and parental
638
rare-element pegmatite systems seemed to predate the Famatinian terrane-continent
639
collision since they display abundant post-emplacement deformation evidences, in
640
disagreement with other pegmatite provinces where a late-stage timing of intrusion is
641
frequent (Černý, 1991b). However, nowadays we interpret that part of the tectonic
642
deformation was produced in a ductile state at the end of the Famatina terrane collision, but
643
the later and superimposed stronger diastrophism was produced partially in brittle state
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during a second collisional episode, situated westward and attributed to the Cuyania
645
accretion (Ramos, 2010).
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7. CONCLUSIONS
648
The S-type leucogranites and associated LCT rare-element pegmatites of the TPD are the
649
results of the episodic anatexis occurred during the late stage of the Famatina terrane-
650
continent collision (≈450-460 Ma). The low-T leucogranites were produced by dominant
651
muscovite dehydration melting and the higher-T leucogranites by muscovite plus incipient
652
biotite dehydration melting of preferably metapelites (±metagraywackes) from the PMC.
653
The leucogranites were intruded in the upper levels of the metamorphic prism at
654
approximately 400-500 MPa. Fractionation of leucogranites derived from muscovite
655
dehydration melts produced dominantly barren, beryl-type and albite-type rare-element
656
pegmatites. Differentiation of the leucogranites produced by muscovite plus biotite
657
dehydration melting generated preferably Li-bearing pegmatites of the albite-spodumene
658
type or spodumene subtype. The regional zoning from leucogranites, pegmatitic
659
leucogranites, barren, beryl-type, albite-spodumene, complex-type spodumene subtype and
660
albite-type pegmatites follows a path toward lower pressures of emplacement and it reflects
661
the fractionation trend of the leucogranites, and the progressive decreasing viscosity of the
662
residual melts. A shear zone separating mica schist and phyllites geological units controlled
663
the ascent and emplacement of the pegmatites. The crystallization of the pegmatites was
664
triggered by rapid undercooling, due to the thermic contrast between the temperatures of
665
the melt and the host-rock, resultant of their fast intrusion. High undercooling, combined
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with high H2O contents and initial subsaturation in volatiles of pegmatitic melts, produced
667
low nucleation rate and fast growth of crystals during periodic resetting of the system
668
traduced in internal zoning achieved in closed chambers of the host rocks in ductile-state.
669
Late stage saturation in H2O and other volatiles, possibly helped to produce part of the rare-
670
element (Be, Nb-Ta) mineralization.
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ACKNOWLEDGEMENTS
673
Several grants of CONICET through different periods and PICT 21638 of FONCYT
674
financed partially the research and are thanked. Teaching, conversations, and insights from
675
many members of the PIG (Pegmatite Interested Group) through the years helped to season
676
the background knowledge and are deeply appreciated. The authors are also very grateful
677
for the constructive reviews of Raúl Lira and Encarnación Roda-Robles. The editorial
678
handling and comments of Víctor Ramos are much appreciated.
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Table 1: Compilation of the most significant dating ages of rocks for the Pringles Metamorphic Complex and the TPD evolution Area Location Rock Sample Method Rock/Mineral Age (Ma) ± 2σ My Reference Virorco Mafic complex Sm-Nd Isochron Whole rock 1002 150 Ferracutti et al. (2017) Metaclastics Sm-Nd Isochron Whole rock 1289 97 Ferracutti et al. (2017) Las Aguilas Felsic seg. in pyrox. JS080f U - Pb SHRIMP Zircon 478 6 Sims et al. (1998) Western Sector Grt-Sil-Gneiss JS129c Th-Pb SHRIMP Monazite 451 10 Sims et al. (1998) Felsic orthogneiss JS079 U-Pb SHRIMP Zircon 484 7 Sims et al. (1998) Mylonite A 56-01 U - Pb SHRIMP Zircon 498 10 Steenken et al. (2011) P. del Tamboreo Granodiorite U - Pb SHRIMP Zircon 470 5 Sims et al. (1997) Paso del Rey Leucogranite Rb - Sr Whole rock 454 21 Llambías et al. (1991) Paso del Rey Leucogranite U - Pb TIMS Zircon 608 +26-25 von Gosen et al. (2002) Paso del Rey N. Leucogranite U - Pb SHRIMP Zircon 456 30 Steenken et al. (2006) Paso del Rey Leucogranite A 02-02 207Pb - 206Pb Evaporation Zircon (older) 597 54 Steenken et al. (2008) Paso del Rey Leucogranite A 02-02 207Pb - 206Pb Evaporation Zircon (rims) 491 19 Steenken et al. (2008) Paso del Rey Leucogranite SLG1 K - Ar Biotite 381 13 Varela et al. (1994) Paso del Rey Leucogranite SLG8 K - Ar Biotite 372 20 Varela et al. (1994) Río La Carpa Leucogranite SLG9 K - Ar Biotite 391 9 Varela et al. (1994) Pegmatite A2-01 K - Ar Muscovite 407.8 8.3 Steenken et al. (2008) Eastern Pegmatite A6-01 K - Ar Muscovite 394.8 8.1 Steenken et al. (2008) Sector Pegmatite A10-01 K - Ar Muscovite 437.5 9.5 Steenken et al. (2008) Pegmatite A15-01 K - Ar Muscovite 408.4 8.6 Steenken et al. (2008) Paso del Rey Pegmatite AH-7 K - Ar Muscovite 398.2 9.2 Lopez de Luchi et al. (2002) Paso del Rey Pegmatite AH-8 K - Ar Muscovite 444.5 9.2 Lopez de Luchi et al. (2002) Victor Hugo Pegmatite VIC-01 K - Ar Muscovite 503 24 Galliski and Linares (1999) C. Canchuleta Pegmatite CAN-01 K - Ar Muscovite 433 24 Galliski and Linares (1999) San Luis I Pegmatite SLI-01 K - Ar Muscovite 317 33 Galliski and Linares (1999) Sta. Ana Pegmatite U - Pb Chemical Uraninite 455 23 Linares (1959) Sta. Ana Pegmatite U - Pb Isotopic Uraninite 460 15 Linares (1959) San Luis II Pegmatite U - Pb LA-ICP-MS Columbite 450 +10-2 v. Quadt and Galliski (2011)
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LT15a LT15b LT16a LT17a LT4c LT5a LT7a LT8c LT10b PR01 PR7 PR8 PR9 PR49 PR353 PR354 PR355 PR357 PR360
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ACCEPTED MANUSCRIPT Table 2: Modal compositions from Cerro La Torre (LT) and Paso del Rey (PR) leucogranites Main minerals Accessories Location Texture Grain size Minor Acc. Kfs Qz Pl Ms Bt Tur-Grt-Ap northern sector granular hypid. coarse 44.7 16.5 36.1 2.7 0.0 tr northern sector granular hypid. coarse 46.1 32.0 15.5 6.4 0.5 tr northern sector pegmatitic very coarse 37.7 54.4 0.0 5.5 3.0 Srl 2.4 northern sector pegmatitic very coarse 42.0 46.0 0.0 12.0 0.0 tr central sector granular hypid. medium 40.1 53.3 0.2 6.4 0.0 tr central sector pegmatitic very coarse 32.7 55.2 1.2 10.7 0.0 Srl .1 central sector granitic to peg. medium - very coarse 43.3 49.4 0.0 7.3 0.0 tr central sector granular hypid. medium to coarse 31.5 61.1 0.2 7.3 0.0 tr central sector granular hypid. medium 32.7 62.1 0.0 4.8 0.0 Grt .4 central sector granular hypid. medium to coarse 36.4 23.5 27.8 10.3 0.9 Srl 1.1 central sector granular hypid. medium to coarse 33.1 32.2 29.6 4.0 0.4 Srl 0.0, Grt 0.5, Ap 0.2 central sector granular hypid. medium to coarse 36.2 25.4 26.4 9.4 0.9 Srl 0.5, Grt 1.0, Ap 0.2 central sector granular hypid. medium to coarse 37.7 27.9 21.6 9.7 1.6 Srl 0.0, Grt 1.3, Ap 0.2 central sector granular hypid. medium to coarse 40.6 23.7 21.5 0.8 0.0 Srl 0.0, Grt 0.5, Sill 12.8 SE sector pegmatitic coarse to very coarse 27.7 53.2 14.6 3.02 0.0 Srl 1.3 Grt 0.2 SE sector granular hypid. medium to coarse 32.6 48.3 11.3 6.4 0.0 Srl 1.4 SE sector pegmatitic coarse to very coarse 34.9 47.6 7.6 4.9 0.0 Srl 5.0 SE sector pegmatitic coarse to very coarse 38.9 45.9 3.6 6.0 0.0 Srl 5.3, Ap 0.2 SE sector pegmatitic very coarse 37.6 47.4 5.9 6.2 0.0 Srl 2.9, Grt 0.09
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Table 3: Chemical Analyses of granitic and metamorphic rocks of the Totoral Pegmatite District Paso del Rey Stock R. Gde. Arenilla Santo Domingo Cerro La Torre Stock1 LT 13 LT 20 LT 25 LT 30 LT07 LT08 AVG M49 M7 M8 M9 M10 PR001 AVG M45 M48 M15 M12 TMLGR TMLGR 2MLGR 2MLGR TMLGR TMLGR TMLGR TMLGR 2MLGRTMLGR TMLGR TMLGR Migm. Gneiss Schist Phyllite 76.34 0.03 13.92 0.58 0.52 0.06 0.10 0.82 4.74 2.36 0.14
63.75 0.07 20.77 1.08 0.97 0.11 0.23 0.62 5.68 6.19 0.33
76.50 0.02 14.10 0.64 0.58 0.05 0.11 0.62 5.67 1.22 0.16
74.64 0.04 13.62 0.54 0.49 0.03 0.08 0.11 1.57 8.05 0.14
74.57 0.03 13.98 0.86 0.77 0.22 0.11 0.84 3.32 4.53 0.12
73.10 0.01 14.27 0.54 0.49 0.26 0.08 0.83 2.99 5.29 0.16
73.22 0.03 13.60 0.57 0.51 0.13 0.13 0.66 3.07 5.49 0.44
73.39 0.04 14.19 0.74 0.67 0.10 0.16 0.47 3.88 4.01 0.38
73.80 0.06 13.99 0.69 0.62 0.06 0.23 0.75 3.64 3.48 0.27
97.49
99.09
98.83
99.09
98.82
98.58
K ppm Ba Rb Sr Cs Ga Tl Be Ta Nb Hf Zr Y Th U W Sn Sb As Cr Ni Co Sc V Cu Pb
41174 19591 51385 10128 66825 37605 37785 43914 45574 33288 28889 225 28 216 12 965 542 331 26 184 132 273 131 52 254 56 155 94 124 112 232 203 156 70 28 58 15 153 174 83 21 46 47 76 6 2 7 3 2 2 4 2 8 10 10 11 10 19 12 9 8 12 8 10 12 12 1 0 1 0 1 0 0 1 1 1 1 1 2 8 6 <1 2 4 <1 3 6 8 1 0 2 1 0 1 1 0 1 2 4 7 5 15 9 5 6 8 1 5 19 10 1 2 2 1 2 1 2 2 1 2 1 33 61 69 19 64 21 45 41 31 53 34 5 5 16 5 2 3 6 1 9 16 12 1 1 3 2 7 1 2 0 1 3 2 1 2 3 2 3 4 3 2 2 2 2 6 1 2 1 1 1 2 1400 1380 1120 1060 4 3 10 3 3 2 4 2 2 6 2 13 <5 <5 <5 <5 <5 <5 <5 <5 <5 6 <5 24 <5 <5 <5 <5 <5 <5 <5 140 130 30 130 110 80 103 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 1 1 1 1 1 1 1 181 158 126 101 2 1 5 0 4 2 2 1 3 3 4 2 2 5 1 2 2 2 2 2 2 6 5 5 5 5 5 5 5 2 2 30 2 55 33 70 18 124 112 69 35 26 21 34
74.93 0.06 14.34 0.71 0.64 0.05 0.19 0.79 3.83 4.29 0.27
1.01 98.54
1.27 98.61
1.16 98.52
1.48 1.31 98.45 100.77
35613 275 211 75 8 12 1 9 2 8 1 32 10 2 2 1200 5 <5 <5 10 10 123 4 10 10 26
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73.36 0.04 14.96 0.72 0.65 0.08 0.12 0.59 3.97 4.55 0.17
74.00 0.06 14.70 0.90 0.81 0.12 0.23 0.49 4.15 4.27 0.28 0.65
73.74 0.04 14.18 0.69 0.58 0.12 0.17 0.67 3.59 4.47 0.30 0.65
73.42 0.61 11.98 3.40 3.06 0.06 1.29 1.29 2.08 3.73 0.09 0.85
58.83 0.94 16.50 8.83 7.95 0.17 3.10 0.54 0.82 3.63 0.09 5.48
64.74 0.74 15.53 5.82 5.24 0.15 2.66 0.67 1.62 3.21 0.13 3.63
61.24 0.82 18.06 6.72 6.05 0.08 2.32 0.31 1.77 4.06 0.15 4.34
98.80
98.93
98.90
99.87
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74.37 0.03 13.35 0.62 0.56 0.01 0.11 0.5 2.86 4.96 0.15 0.53
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SiO2 % TiO2 Al2O3 Fe2O3 FeOt calc. MnO MgO CaO Na2O K2O P2O5 LOI H2O wt. Total
SC
Location Sample Rock
99.85
250 220 40 17 --10 2 8 1 20 8 2 2 5 -0 1 170 5 5 3 8 5 32
37456 30964 30134 26647 33703 190 787 471 433 535 189 141 185 145 189 51 182 48 85 69 9 3 10 10 13 11 13 26 19 24 1 0 1 0 1 7 <1 3 3 4 2 1 1 2 2 9 14 17 15 17 1 8 6 5 5 35 298 194 168 164 9 21 35 16 34 2 15 19 13 17 2 3 4 4 3 1028 316 443 895 136 2 7 5 7 0 <5 <5 <5 <5 1 <5 <5 <5 <5 37 40 80 70 80 9 10 30 30 40 116 29 64 107 41 3 8 18 14 17 5 61 138 97 119 8 2 2 20 40 29 15 3 7 13
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10
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30
10
10
10
13
10
10
10
10
10
24
12
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90
La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
2.2 4.2 0.5 1.6 0.4 0.2 0.5 0.1 0.7 0.1 0.4 0.1 0.6 0.1
3.2 5.4 6.0 1.9 0.5 0.1 0.5 0.1 0.8 0.1 0.5 0.1 0.8 0.1
6.8 13.2 1.4 5.1 1.5 0.3 1.6 0.4 2.6 0.5 1.5 0.3 2.0 0.3
5.0 8.9 1.0 3.3 0.8 0.1 0.6 0.1 0.8 0.1 0.4 0.1 0.7 0.1
1.6 2.7 0.3 1.0 0.2 0.3 0.2 0.1 0.3 0.1 0.2 0.1 0.4 0.1
4.3 7.2 0.7 2.2 0.5 0.3 0.3 0.1 0.5 0.1 0.4 0.1 0.9 0.1
3.9 6.9 0.7 2.5 0.7 0.2 0.6 0.2 1.0 0.2 0.6 0.1 0.9 0.1
2.2 4.0 0.4 1.0 0.2 0.1 0.2 0.1 0.5 0.1 0.5 0.1 1.1 0.2
4.2 8.3 0.9 3.2 0.9 0.3 0.9 0.2 1.6 0.3 0.9 0.1 1.1 0.1
7.5 16.5 1.9 7.0 1.9 0.2 1.4 0.5 2.8 0.5 1.5 0.2 1.3 0.2
5.2 11.0 1.2 4.6 1.3 0.3 0.9 0.3 2.0 0.4 1.1 0.2 1.2 0.2
6.3 12.9 1.4 4.9 1.4 0.4 1.2 0.4 2.2 0.4 1.2 0.3 1.3 0.2
4.2 9.0 -4.0 1.0 0.3 -0.2 ----1.2 0.2
4.9 10.3 1.1 4.1 1.1 0.3 0.9 0.3 1.8 0.3 1.0 0.2 1.2 0.2
37.4 78.7 9.2 36.6 7.3 1.3 5.3 0.8 4.2 0.8 2.1 0.3 2.3 0.3
47.4 99.6 10.9 43.3 8.6 1.5 6.7 1.2 6.4 1.3 3.5 0.5 3.4 0.5
12.3 60.8 2.7 9.3 2.0 0.4 1.7 0.4 2.7 0.7 2.3 0.4 2.7 0.4
50.1 100.0 10.7 37.5 7.7 1.4 6.2 1.1 6.4 1.3 3.6 0.6 3.6 0.5
∑REE LREE HREE (La/Lu)N (La/Sm)N (Lu/Gd)N Eu/Eu*
11.6 8.9 2.6 2.6 3.4 1.4 1.4
14.7 11.6 3.0 3.1 4.0 1.7 0.7
37.5 28.0 9.2 2.6 2.8 1.4 0.6
22.0 19.0 2.9 5.3 3.9 1.3 0.4
7.5 5.8 1.4 2.4 5.0 2.8 4.7
17.7 14.9 2.5 3.5 5.4 3.4 2.1
18.5 14.7 3.6 3.2 4.1 2.0 1.7
10.6 7.8 2.8 1.4 6.9 6.7 0.9
23.1 17.5 5.3 3.2 2.9 1.2 1.0
43.4 34.8 8.4 4.7 2.5 1.0 0.4
29.9 23.3 6.3 3.0 2.5 1.6 0.8
34.4 26.9 7.1 3.7 2.8 1.2 0.8
20.1 18.2 1.6
26.9 21.4 5.2 3.2 3.5 2.3 0.8
186.6 169.2 16.1 12.0 3.2 0.5 0.6
234.8 209.8 23.5 10.4 3.4 0.6 0.6
98.8 87.1 11.3 3.2 3.8 1.9 0.7
230.7 206.0 23.3 10.6 4.1 0.6 0.6
ASI FeO+MgO K/(K+Na) K/Rb Nb/Ta #Ta Zr/Hf Rb/Sr Rb/Ba Rb/Cs TºC (Zr) TºC (REE)
1.20 0.67 0.53 314.3 14.0 0.07 27.5 1.9 0.6 21.8 679 634
1.19 0.62 0.25 376.8 12.5 0.07 30.5 1.9 1.9 23.6 721 645
1.24 1.20 0.42 202.3 7.9 0.11 30.0 4.4 1.2 37.9 716 698
1.22 0.69 0.12 180.9 8.2 0.11 23.8 3.7 4.7 18.7 641 680
1.20 0.57 0.77 431.1 16.7 0.06 30.5 1.0 0.2 67.4 725 603
1.11 0.88 0.44 400.1 12.0 0.08 23.3 0.5 0.2 62.7 640 648
1.20 0.77 0.42 317.6 11.9 0.08 27.6 1.5 1.4 38.7 696 659
1.19 0.57 0.54 392.1 3.3 0.23 25.6 5.3 4.3 65.9 691 621
1.17 0.64 0.54 196.4 4.5 0.18 28.2 5.0 1.3 29.7 667 663
1.28 0.83 0.40 164.0 8.6 0.10 35.3 4.3 1.5 21.6 713 727
1.30 0.85 0.39 185.2 2.6 0.28 28.3 2.1 0.6 16.4 683 700
1.19 0.83 0.42 168.8 4.7 0.18 29.1 2.8 0.8 25.1 672 697
1.22 0.23 0.40 0.0 4.4 0.18 15.4 5.5 0.9 13.0 642 673
1.22 0.66 0.45 184.4 4.8 0.19 27.0 3.7 1.6 28.6 680 687
1.24
2.68
2.16
2.35
0.54 219.6 15.6 0.06 38.2 0.8 0.2 41.5
0.74 162.9 12.1 0.08 34.6 3.9 0.4 17.8
0.57 183.8 10.0 0.09 34.3 1.7 0.3 13.9
0.60 178.3 10.6 0.09 34.2 2.7 0.4 14.7
2
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Zn
Major and trace elements of LT analyses were taken from Oyarzábal (2004). PR001 results were taken from Galliski (1994b). Great part of the high W, Cr and Co contents of PR leucogranites and metamorphics is due to contamination during milling with a WC ring mill equipment.
ACCEPTED MANUSCRIPT Table 4: Main rare-element pegmatites of the Totoral pegmatite district 80 62 150 30 22 55 15 190 >300 120 90 105 23 23 43 14.5 50 55 35 ~10 32 70 45 90 22 48 50 150 50 730 20 98 32 45 18
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Type
Subtype
15 Beryl Brl-Col-Pho 32 Beryl Brl-Col-Pho 42 Beryl Brl-Col-Pho 6 Beryl Brl-Col-Pho 14 Beryl Brl-Col-Pho 21 Beryl Brl-Col-Pho 8 Beryl Brl-Col-Pho 12 Albite 30 Albite 21 Beryl Brl-Col-Pho 7 Beryl Brl-Col-Pho 12 Barren (Brl) 4 Barren (Brl) 7.5 Barren 5.5 Barren (Brl) 4 Barren 20 Beryl Brl-Col-Pho 25 Beryl (Brl-Col) 6 Beryl (Brl-Col) 2 Beryl (Brl-Col) 5.5 Beryl (Brl-Col) 20 Beryl Brl-Col-Pho 15 Beryl (Brl-Col) 12 Beryl (Brl-Col) Beryl (Brl-Col) 5 Beryl (Brl-Col) 4 Beryl (Brl-Col) 6 Beryl 4 4 Complex Spodumene 2 to 35 Ab-Spodumene 7 Complex Spodumene 5 Ab-Spodumene 4 Ab-Spodumene 6 Complex Spodumene 5 Complex Spodumene
Mined for
Mining state
Brl Brl-Kfs-Ms Brl-Kfs-Ms Brl-Kfs-Ms Brl Brl-Kfs-Col Brl Ms-Ab Ab-Brl-Col Brl Brl-Kfs Kfs-Qz-Ms Kfs-Qz -Ms Kfs-Qz -Ms not mined Kfs-Qz -Ms Brl-Kfs-Qz Brl Brl Ms Brl Brl-Kfs-Qz Brl-Kfs Brl-Ms Tant Brl Brl Brl Spd Spd Spd Spd Spd Spd Col-Spd
inactive temp. active temp. active temp. active inactive inactive inactive inactive inactive inactive inactive active inactive inactive inactive inactive inactive inactive inactive inactive inactive inactive inactive inactive inactive inactive inactive inactive exploration exploration exploration exploration exploration inactive inactive
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tabular elipsoidal tabular lenticular lenticular tabular lenticular tabular subtabular tabular tabular tabular tabular tabular tabular tabular lenticular tabular tabular tabular tabular tabular tabular tabular tabular tabular tabular tabular tabular tabular tabular tabular lenticular lenticular tabular
Width
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La Titina Santa Ana La Empleada Los Aleros Devel Cerro La Torre Los Chilenitos Nueve de Julio Aquelarre Ind. Argentina La Betita La Tinita La Vistosa La Vistosa II La Vistosa III La Vistosa IV La Vistosa V Ranquel Loma Alta Ranquel II Don Lito San Ign. Loyola La China C. Canchuleta Tito San Cayetano La Argentina Franci Juan Héctor La Rioja San Fernando Paso del Rey San Luis I San Luis II Teresaida La Nilda Diana Víctor Hugo
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Title: METALLOGENESIS OF THE TOTORAL LCT RARE-ELEMENT PEGMATITE DISTRICT, SAN LUIS, ARGENTINA: A REVIEW
The TPD is formed by S-type leucogranites and rare-element pegmatites.
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•
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Highlights:
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• The leucogranites form an Ordovician bimodal suite of anatectic collisional origin.
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Regional pegmatite zoning follows the fractionation trend of the parental granites.
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The Li-Ta resources are linked to pegmatites fractionated from high-T
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leucogranites.